​MN 98 Vasettha Sutta: To Vasettha 

Thus have i heard. 

On one occasion the Blessed One was living at Icchanangala, in the wood near Icchanangala. Now on that occasion a number of well-known, well-to-do brahmins were staying at Icchanangala, that is, the brahmin Canki, the brahmin Tarukkha, the brahmin Pokkharasati, the brahmin Janussoni, the brahmin Todeyya, and other wellknown, well-to-do brahmins. Then, while the brahmin students Vasettha and Bharadvaja were walking and wandering for exercise, this discussion arose between them: "How is one a brahmin?"

The brahmin student Bharadvaja said: "When one is well-born on both sides, of pure maternal and paternal descent seven generations back, unassailable and impeccable in respect of birth, then one is a brahmin."
The brahmin student Vasettha said: "When one is virtuous and fulfills the observances, then one is a brahmin."
But the brahmin student Bharadvaja could not convince the brahmin student Vasettha, nor could the brahmin student Vasettha convince the brahmin student Bharadvaja.

Then the brahmin student Vasettha addressed the brahmin student Bharadvaja: "Sir, the recluse Gotama, the son of the Sakyans who went forth from a Sakyan clan, is living at Icchanangala, in the wood near Icchanangala. 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, blessed.' Come, Bharadvaja, let us go to the recluse Gotama and ask him about this matter. As he answers, so we will remember it."
"Yes, sir," the brahmin student Bharadvaja replied. 

Then the two brahmin students, Vasettha and Bharadvaja, went to the Blessed One and exchanged greetings with him. When this courteous and amiable talk was finished, they sat down at one side and the brahmin student Vasettha addressed the Blessed One in stanzas thus: 

Vasettha
"We are both acknowledged to possess The knowledge we claim of the Triple Veda,
For I am Pokkharasati's pupil And he a pupil of Tarukkha. 

We have attained full mastery Over all that the Vedic experts teach;
Skilled in philology and grammar We match our teachers in discussion.

A dispute has arisen between us, Gotama, Concerning the question of birth and class:
Bharadvaja says one is a brahmin by birth, While I hold one is a brahmin by action.
Know this, O Seer, as our debate. 

Since neither of us could convince the other, Or make him see his point of view,
We have come to ask you, sir, Widely famed to be a Buddha. 

As people turn with palms upraised Towards the moon when it reaches fullness,
So in the world do they venerate you And pay homage to you, Gotama. 

So now we ask of you, Gotama, The eye uprisen in the world: Is one a brahmin by birth or action?
Explain to us who do not know How we should recognize a brahmin." 

Buddha

"I will explain to you as they really are, Vasettha" said the Blessed One,
"The generic divisions of living beings; For many are the kinds of birth. 

Know first the grass and trees: Though they lack self-awareness,
Their birth is their distinctive mark; For many are the kinds of birth.

Next come the moths and butterflies And so on through as far as ants:
Their birth is their distinctive mark; For many are the kinds of birth. 

Then know the kinds of quadrupeds of varied sorts both small and large:
Their birth is their distinctive mark; For many are the kinds of birth. 

Know those whose bellies are their feet, To wit, the long-backed class of snakes:
Their birth is their distinctive mark; For many are the kinds of birth. 

Know too the water-dwelling fish That pasture in the liquid world:
Their birth is their distinctive mark; For many are the kinds of birth. 

Next know the birds that wing their way As they range in open skies:
Their birth is their distinctive mark; For many are the kinds of birth. 

 "While in these births the differences Of birth make their distinctive mark,
With humans no differences of birth Make a distinctive mark in them. 

Nor in the hairs nor in the head Nor in the ears nor in the eyes
Nor in the mouth nor in the nose Nor in the lips nor in the brows; 

Nor in the shoulders or the neck Nor in the belly or the back
Nor in the buttocks or the breast Nor in the anus or genitals; 

Nor in the hands nor in the feet Nor in the fingers or the nails
Nor in the knees nor in the thighs Nor in their color or in voice:
Here birth makes no distinctive mark As with the other kinds of birth.

In human bodies in themselves Nothing distinctive can be found.
Distinction among human beings Is purely verbal designation.

"Who makes his living among men By agriculture, you should know Is called a farmer,
Vasettha; He is not a brahmin. 

Who makes his living among men By varied crafts, you should know Is called a craftsman,
Vasettha; He is not a brahmin. 

Who makes his living among men By merchandise, you should know Is called a merchant,
Vasettha; He is not a brahmin. 

Who makes his living among men By serving others, you should know Is called a servant,
Vasettha; He is not a brahmin. 

Who makes his living among men By stealing, you should know Is called a robber, Vasettha; He is not a brahmin. 
Who makes his living among men By archery, you should know Is called a soldier, Vasettha; He is not a brahmin. 
Who makes his living among men By priestly craft, you should know Is called a chaplain, Vasettha; He is not a brahmin. 
Whoever governs among men The town and realm, you should know Is called a ruler, Vasettha; He is not a brahmin.
 
"I call him not a brahmin Because of his origin and lineage. If impediments still lurk in him,
He is just one who says 'Sir.'Who is unimpeded and clings no more: He is the one I call a brahmin. 

Who has cut off all fetters And is no more by anguish shaken,
Who has overcome all ties, detached: He is the one I call a brahmin.

Who has cut each strap and thong, The reins and bridle-band as well, 
Whose shaft is lifted, the awakened one: He is the one I call a brahmin. 

Who endures without a trace of hate Abuse, violence, and bondage too,
With strength of patience well arrayed: He is the one I call a brahmin. 

Who does not flare up with anger, Dutiful, virtuous, and humble,
Subdued, bearing his final body: He is the one I call a brahmin. 

Who, like the rain on lotus leaves, Or mustard seed on the point of an awl,
Clings not at all to sensual pleasures: He is the one I call a brahmin. 

Who knows right here within himself The destruction of all suffering,
With burden lowered, and detached: He is the one I call a brahmin. 

Who with deep understanding, wise, Can tell the path from the not-path
And has attained the goal supreme: He is the one I call a brahmin. 

Aloof alike from householders And those gone into homelessness,
Who wanders without home or wish: He is the one I call a brahmin. 

Who has laid aside the rod Against all beings frail or bold,
Who does not kill or have them killed: He is the one I call a brahmin. 

Who is unopposed among opponents, Peaceful among those given to violence, 
Who does not cling among those who cling: He is the one I call a brahmin. 

Who has dropped all lust and hate, Dropped conceit and contempt,
Like mustard seed on the point of an awl: He is the one I call a brahmin.

Who utters speech free from harshness, Full of meaning, ever truthful,
Which does not damage anyone: He is the one I call a brahmin. 

Who in the world will never take What is not given, long or short,
Small or big or fair or foul: He is the one I call a brahmin. 

Who has no more inner yearnings Regarding this world and the next,
Who lives unyearning and detached: He is the one I call a brahmin. 

Who has no more indulgences No more perplexity since he knows
Through having reached the Deathless Sphere: He is the one I call a brahmin. 

Who, by transcending all ties here About both merit and evil deeds,
Is sorrowless, stainless, and pure: He is the one I call a brahmin. 

Who, pure as the spotless moon, Is clear and limpid,
and in whom Delight and being have been destroyed: He is the one I call a brahmin. 

Who has passed beyond the swamp, The mire, samsara, all delusion, 
Who has crossed to the further shore And meditates within the jhanas,
Is unperturbed and unperplexed, Attained Nibbana through no clinging:
He is the one I call a brahmin. 

Who has abandoned sensual pleasures And wanders here in homelessness
With sense desires and being destroyed: He is the one I call a brahmin. 

Who has abandoned craving too, And wanders here in homelessness,
With craving and being both destroyed: He is the one I call a brahmin. 

Who leaves behind all human bonds And has cast off the bonds of heaven,
Detached from all bonds everywhere: He is the one I call a brahmin. 

Who leaves behind delight and discontent, Who is cool and without attachment,
The hero who has transcended the whole world: He is the one I call a brahmin.

Who knows how beings pass away To reappear in many a mode,
Unclutching he, sublime, awake: He is the one I call a brahmin. 

Whose destination is unknown To gods, to spirits, and to men,
An arahant with taints destroyed: He is the one I call a brahmin. 

Who has no impediments at all, Before, behind, or in the middle,
Who is unimpeded and clings no more: He is the one I call a brahmin. 

 The herd's leader, perfected hero, The great seer whose victory is won,
Unperturbed, cleansed, awakened: He is the one I call a brahmin. 

Who knows his manifold past lives And sees the heavens and states of woe,
Who has reached the destruction of birth: He is the one I call a brahmin. 

"For name and clan are assigned As mere designations in the world;
Originating in conventions, They are assigned here and there. 

For those who do not know this fact, Wrong views have long underlain their hearts;
Not knowing, they declare to us: 'One is a brahmin by birth.' 

One is not a brahmin by birth, Nor by birth a non-brahmin.
By action is one a brahmin, By action is one a non-brahmin. 

For men are farmers by their acts, And by their acts are craftsmen too;
And men are merchants by their acts, And by their acts are servants too. 

And men are robbers by their acts, And by their acts are soldiers too;
And men are chaplains by their acts, And by their acts are rulers too. 

"So that is how the truly wise, see action as it really is, 
Seers of dependent origination, Skilled in action and its results.

Action makes the world go round, Action makes this generation turn.
Living beings are bound by action Like the chariot wheel by the pin.

Asceticism, the holy life, Self-control and inner training
By this one becomes a brahmin, In this supreme brahminhood lies.

One possessing the triple knowledge, Peaceful, with being all destroyed:
Know him thus, O Vasettha, As Brahma and Sakka for those who understand." 

When this was said, the brahmin students Vasettha and Bharadvaja said to the Blessed One: "Magnificent, Master Gotama! Magnificent, Master Gotama!...From today let Master Gotama remember us as lay followers who have gone to him for refuge for life." 

In summary, at Icchanakala there were two young brahmins, Vāsettha and Bhāradvāja who were arguing on what makes a true brahmin. Bhāradvāja maintained that it was pure descent from seven generations of ancestors, with neither break nor blemish in the lineage, whereas Vāsettha contended that virtue and moral behaviour made a true brahmin. As neither could convince the other, they agreed to refer the matter to the Buddha, who said it was not by birth but by one's own actions which made the true brahmin. Buddha replied Vasettha in verses that people are classified by their occupations but there is no one more superior than another because of birth. A true brahmin is one who is virtuous, abandoned cravings, destroyed all taints, practiced the noble eightfold path. 

References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The middle length discourses of the Buddha (Bhikkhu Bodhi)