​MN 92 Sela Sutta: To Sela 

Thus have i heard. 

On one occasion the Blessed One was wandering in the country of the Anguttarapans with a large Sangha of bhikkhus, with 1250 bhikkhus, and eventually he arrived at a town of the Anguttarapans named Apana. The matted-hair ascetic Keniya heard: "The recluse Gotama, the son of the Sakyans who went forth from a Sakyan clan, has been wandering in the country of the Anguttarapans with a large Sangha of bhikkhus, with 1250 bhikkhus, and he has come to Apana. Now a good report of Master Gotama has been spread to this effect...(AS Sutta 91).. .Now it is good to see such arahants."

Then the matted-hair ascetic Keniya went to the Blessed One and exchanged greetings with him, and when this courteous and amiable talk was finished, he sat down at one side. The Blessed One instructed, urged, roused, and encouraged him with a talk on the Dhamma. Then, having been instructed, urged, roused, and encouraged by the Blessed One with a talk on the Dhamma, the matted-hair ascetic Keniya said to the Blessed One: "Let Master Gotama together with the Sangha of bhikkhus consent to accept tomorrow's meal from me." When this was said, the Blessed One told him: "The Sangha of bhikkhus is large, Keniya, consisting of 1250 bhikkhus, and you place full confidence in the brahmins." A second time the matted-hair ascetic Keniya said to the Blessed One: "Although the Sangha of bhikkhus is large, Master Gotama, consisting of 1250 bhikkhus, and although I place full confidence in the brahmins, still let Master Gotama, together with the Sangha of bhikkhus, consent to accept tomorrow's meal from me." A second time the Blessed One told him: "The Sangha of bhikkhus is large, Keniya..."
 A third time the matted-hair ascetic Keniya said to the Blessed One: "Although the Sangha is large, Master Gotama...still let Master Gotama together with the Sangha of bhikkhus consent to accept tomorrow's meal from me." The Blessed One consented in silence.

Then, knowing that the Blessed One had consented, the matted-hair ascetic Keniya rose from his seat and went to his own hermitage where he addressed his friends and companions, his kinsmen and relatives thus: "Hear me, sirs, my friends and companions, my kinsmen and relatives. The recluse Gotama has been invited by me for tomorrow's meal together with the Sangha of bhikkhus. Make the necessary purchases and preparations for me." "Yes, sir," they replied, and some dug out ovens, some chopped wood, some washed dishes, some set out water jugs, some prepared seats, while the matted-hair ascetic Keniya himself set up a pavilion.

Now on that occasion the brahmin Sela was staying at Apana. He was a master of the Three Vedas with their vocabularies, liturgy, phonology, and etymology, and the histories as a fifth; skilled in philology and grammar, he was fully versed in natural philosophy and in the marks of a Great Man, and was teaching the recitation of the hymns to three hundred brahmin students. At the time the matted-hair ascetic Keniya had placed full confidence in the brahmin Sela. Then the brahmin Sela, while walking and wandering for exercise attended by his 300 brahmin students, came to the matted-hair ascetic Keniya's hermitage. There he saw some men digging out ovens, some chopping wood, some washing dishes, some setting out water jugs, some preparing seats, while the matted-hair ascetic Keniya himself was setting up a pavilion.

When brahmin sela saw this, he asked the matted-hair ascetic Keniya: "What, is Master Keniya to hold a marriage or a giving in marriage? Or is there some great sacrifice? Or has King Seniya Bimbisara of Magadha been invited with a large retinue for tomorrow's meal?"
Keniya: "I will not be holding a marriage or a giving in marriage, Master Sela, nor has King Seniya Bimbisara of Magadha been invited with a large retinue for tomorrow's meal, but I am planning a great sacrifice. The recluse Gotama, the son of the Sakyans who went forth from a Sakyan clan, has been wandering in the country of the Anguttarapans with a large Sangha of 1250 bhikkhus and has come to Apana. Now a good report of Master Gotama has been spread to this effect: 'That Blessed One is accomplished, fully enlightened, perfect in true knowledge and conduct, sublime, knower of worlds, incomparable leader of persons to be tamed, teacher of gods and humans, enlightened buddha, blessed.' He has been invited by me for tomorrow's meal together with the Sangha of bhikkhus."

Brahmin Sela: "Did you say 'Buddha,' Keniya?"
Keniya: "I said 'Buddha,' Sela."
Brahmin Sela: "Did you say 'Buddha,' Keniya?"
Keniya: "I said 'Buddha, Sela."
Then it occurred to the brahmin Sela: "Even this word 'Buddha' is hard to come across in this world. Now the thirty two marks of a Great Man have been handed down in our hymns, and the Great Man who is endowed with them has only two possible destinies, no other. If he lives the home life he becomes a Wheel-turning Monarch, a righteous king who rules by the Dhamma, master of the four quarters, all-victorious, who has stabilized his country and possesses the seven treasures. He has these seven treasures: the wheel-treasure, the elephant treasure, the horse-treasure, the jewel-treasure, the woman treasure, the steward-treasure, and the counselor-treasure as the seventh. His children, who exceed a thousand, are brave and heroic and crush the armies of others; over this earth bounded by the ocean he rules without a rod, without a weapon, by means of the Dhamma. But if he goes forth from the home life into homelessness, he becomes an Accomplished One, a Fully Enlightened One, who draws aside the veil in the world."

Brahmin Sela: "My good Keniya, where is Master Gotama, the Accomplished One, the Fully Enlightened One, now living?" When this was said, the matted-hair ascetic Keniya extended his right arm and said:"There, where that green line of the grove is, Master Sela." Then the brahmin Sela went with the 300 brahmin students to the Blessed One. He addressed the brahmin students: "Come quietly, sirs, tread carefully; for these Blessed ​Ones are difficult to approach, they wander alone like lions. When I am speaking with the recluse Gotama, do not break in and interrupt me, but wait until our talk is finished." 
Then the brahmin Sela went to the Blessed One and exchanged greetings with him. When this courteous and amiable talk was finished, he sat down at one side and looked for the thirty-two marks of a Great Man on the Blessed One's body. He saw, more or less, the thirty-two marks of a Great Man on the Blessed One's body, except two; he was doubtful and uncertain about two of the marks, and he could not decide and make up his mind about them: about the male organ being enclosed in a sheath and about the largeness of the tongue.

Then it occurred to the Blessed One: "This brahmin Sela sees the thirty-two marks of a Great Man on me, except two; he is doubtful and uncertain about two of the marks, and he cannot decide and make up his mind about them: about the male organ being enclosed in a sheath and about the largeness of the tongue." Then the Blessed One worked such a feat of supernormal power that the brahmin Sela saw that the Blessed One's male organ was enclosed in a sheath. Next the Blessed One extruded his tongue, and he repeatedly touched both ear holes and both nostrils, and he covered the whole of his forehead with his tongue.

Then the brahmin Sela thought: "The recluse Gotama is endowed with the thirty-two marks of a Great Man; they are complete, not incomplete. But I do not know whether he is a Buddha or not. However, I have heard from elder aged brahmins who speak according to the lineage of teachers that those who are the Accomplished Ones, Fully Enlightened Ones, reveal themselves as such when their praise is spoken. Suppose I extol the recluse Gotama to his face with fitting stanzas."

Then Sela extolled the Blessed One to his face with fitting stanzas:  
"O perfect in body, well favored, Well fashioned and lovely to behold; O Blessed One, golden is your color,
And white your teeth; you are strong. The features are seen one and all That distinguish a man as well born; 
They are all to be found on your body, These marks that reveal a Great Man.
With eyes clear, with countenance bright, Majestic, erect as a flame,
In the midst of this body of recluses You shine like the blazing sun.
A bhikkhu so lovely to look on With skin of so golden a sheen With beauty so rare
why should you Be content with the life of a recluse?
You are fit to be a king, a lord of chariots, A monarch who makes the wheel turn,
A victor in all the four quarters And lord of the Jambu-tree Grove
With warriors and great princes All devoted to your service,
​O Gotama, you should reign As ruler of men, king above all kings." 
 Buddha:
"I am already a king, O Sela," the Blessed One replied.
"I am supreme king of the Dhamma,I make the Wheel of Dhamma revolve, The wheel that none can stop." 

Sela:
"You claim full enlightenment," the brahmin Sela said,
"You tell me, O Gotama, 'I am supreme long of the Dhamma, I make the Wheel of Dhamma revolve.' 
Who is your general, that disciple Who follows in the Master's own way?
Who is it who helps you to turn The wheel set in motion by you?" 

Buddha:
"The wheel set in motion by me," The Blessed One replied, 
"That same supreme Wheel of Dhamma, Sariputta the Tathagata's son Helps me in turning this wheel. 
What must be known is directly known, What must be developed has been developed,
What must be abandoned has been abandoned, Therefore, brahmin, I am a Buddha. 

So let your doubts about me cease And let decision take their place,
For it is always hard to gain Sight of the Enlightened Ones.

I am the one whose presence in the world Is very rarely come upon,
I am the Fully Enlightened One, I, O brahmin, am the supreme physician. 
I am the holy one beyond compare Who has crushed all Mara's teeming hordes;
Having defeated all my enemies, I rejoice free from fear." 

Sela"
"O sirs, hear this, hear what he says, The man of vision, the physician,
The mighty hero who roars Like a lion in the forest. 
Who, even though of outcast birth, Would not believe him when he saw
That he is the holy one beyond compare Who has crushed all Mara's teeming hordes? 

Now let him follow me who wants And who wants not, let him depart.
For I will go forth under him, This man of lofty wisdom." 
 Pupils:
"If, O sir, you now approve This teaching of the Enlightened One,
We too will go forth under him, This man of lofty wisdom." 

Sela:
"There are three hundred brahmins here Who with uplifted hands implore:
'O may we live the holy life Under you, O Blessed One.'" 

Buddha:
"The holy life is well proclaimed, O Sela," said the Blessed One,
"To be seen here and not delayed; One who trains with diligence Will find a fruitful going forth." 

Then the brahmin Sela and his assembly received the going forth under the Blessed One, and they received the full admission. Then, when the night had ended, the matted-hair ascetic Keniya had good food of various kinds prepared in his own hermitage and had the time announced to the Blessed One: "It is time, Master Gotama, the meal is ready." Then, it being morning, the Blessed One dressed, and taking his bowl and outer robe, he went with the Sangha of bhikkhus to the hermitage of the matted-hair ascetic Keniya and sat down on the seat made ready.

Then, with his own hands, the matted-hair ascetic Keniya served and satisfied the Sangha of bhikkhus headed by the Buddha with various kinds of good food. When the Blessed One had eaten and had withdrawn his hand from the bowl, the matted-hair ascetic Keniya took a low seat and sat down on one side. Thereupon the Blessed One gave him his blessing with these stanzas: 

"Burnt offerings are the glory of fires, Savitri the glory of Vedic hymns,
Glory of human beings, a king, Glory of flowing rivers, the sea; 
The moon is the glory of the stars, The sun is the glory of all that shine;
Merit is the glory of all who aspire; The Sangha, glory of those who give," 
When the Blessed One had given his blessing with these stanzas, he rose from his seat and departed.

Then, not long after their full admission, dwelling alone, withdrawn, diligent, ardent, and resolute, the venerable Sela and his assembly, by realising for themselves with direct knowledge, here and now entered upon and abided in that supreme goal of the holy life for the sake of which clansmen rightly go forth from the home life into homelessness. They directly knew: "Birth is destroyed, the holy life has been lived, what had to be done has been done, there is no more coming to any state of being."

And the venerable Sela together with his assembly became arahants. Then the venerable Sela together with his assembly went to the Blessed One. Having arranged his upper robe on one shoulder, extending his hands in reverential greeting towards the Blessed One, he addressed him with these stanzas: 
"Eight days have passed, All-Seeing One, Since we went to you for refuge.
In these seven nights, O Blessed One, We have been tamed in your teaching. 
You are the Buddha, you are the Teacher, You are the Sage, the conqueror of Mara.
Having cut off all evil tendencies, You have crossed and guide humanity across. 
You have surmounted all attachments, You have removed all the taints.
You are a lion free from clinging, You have abandoned fear and dread. 
Here these three hundred bhikkhus stand With hands held out in adoration.
O Hero, extend your feet, And let these great beings worship the Teacher." 
In this discourse, a matted hair ascetic named Keniya was greatly satisfied by a teaching of the Buddha and invited him and the order of 1200 bhikkhus to a meal for the next day. In the meantime, a brahmin Sela saw the preparations for the meal being made by Keniya and is told that it is for an Awakened One, the fully enlightened Buddha. Brahmin Sela is stirred by the idea of an Awakened One, the Buddha and paid a visit to the Buddha immediately with his 300 followers.

The brahmin Sela questions the Buddha, gains faith in him, and becomes a monk along with his company of pupils. 
The next day the Buddha and the order of bhikkhus, some 1500 in number show up for the meal at Keniya's place. Not long after ordination, Sela and his 300 followers achieved arahantship and they paid respect and honor the buddha. ​
References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The Middle discourses of the Buddha (Bhikkhu Bodhi)