​MN 146 Nandakovada Sutta: Advice from Nandaka 

Thus have i heard. 

On one occasion the Blessed One was living at Savatthi in Jeta's Grove, Anathapindika's Park. Then Mahapajapati Gotami together with five hundred bhikkhunis went to the Blessed One. After paying homage to the Blessed One, she stood at one side and said to him: "Venerable sir, let the Blessed One advise the bhikkhunis, let the Blessed One instruct the bhikkhunis, let the Blessed One give the bhikkhunis a talk on the Dhamma."

Now on that occasion the elder bhikkhus were taking turns in advising the bhikkhunis, but the venerable Nandaka did not want to advise them when his turn came. Then the Blessed One addressed the venerable Ananda: "Ananda, whose turn is it today to advise the bhikkhunis?"
Ananda :"Venerable sir, it is the venerable Nandaka's turn to advise the bhikkhunls, but he doesn't want to advise them even though it is his turn."

Then the Blessed One addressed the venerable Nandaka: "Advise the bhikkhunis, Nandaka. Instruct the bhikkhunis, Nandaka. Give the bhikkhunis a talk on the Dhamma, brahmin."
"Yes, venerable sir,"the venerable Nandaka replied. Then, in the morning, the venerable Nandaka dressed, and taking his bowl and outer robe, went into Savatthi for alms. After that he went with a companion to the Rajaka Park. The bhikkhunis saw the venerable Nandaka coming in the distance and prepared a seat and set out water for the feet. The venerable Nandaka sat down on the seat made ready and washed his feet. The bhikkhunis paid homage to him and sat down at one side.

When they were seated, the venerable Nandaka told the bhikkhunis: "Sisters, this talk will be in the form of questions. When you understand you should say: 'We understand'; when you do not understand you should say: 'We do not understand'; when you are doubtful or perplexed you should ask me: 'How is this, venerable sir? What is the meaning of this?'"
Bhikkhunis: "Venerable sir, we are satisfied and pleased with the master Nandaka for inviting us in this way."
Nandaka: "Sisters, what do you think? Is the eye permanent or impermanent?"
Bhikkunis:"Impermanent, venerable sir."
Nandaka: "Is what is impermanent suffering or happiness?"
Bhikkunis: "Suffering, venerable sir."
Nandaka: "Is what is impermanent, suffering, and subject to change fit to be regarded thus: 'This is mine, this I am, this is my self'?"
Bhikkunis: "No, venerable sir."

Nandaka: "Sisters, what do you think? Is the ear...the nose...the tongue...the body...the mind permanent or impermanent?"
Bhikkunis : "Impermanent, venerable sir."
Nandaka: "Is what is impermanent suffering or happiness?"
Bhikkunis: "Suffering, venerable sir."
Nandaka: "Is what is impermanent, suffering, and subject to change fit to be regarded thus: 'This is mine, this I am, this is my self'?"
Bhikkunis: "No, venerable sir. Why is that? Because, venerable sir, we have already seen this well as it actually is with proper wisdom thus: 'These six internal bases are impermanent.'"

Nandaka: "Good, good, sisters! So it is with a noble disciple who sees this as it actually is with proper wisdom. Sisters, what do you think? Are forms...sounds...odors... flavors...tangibles...mind-objects permanent or impermanent?"
Bhikkunis: "Impermanent, venerable sir."
Nandaka: "Is what is impermanent suffering or happiness?"
Bhikkunis: "Suffering, venerable sir."
Nandaka: "Is what is impermanent, suffering, and subject to change fit to be regarded thus: 'This is mine, this I am, this is my self'?"
Bhikkunis: "No, venerable sir. Why is that? Because, venerable sir, we have already seen this well as it actually is with proper wisdom thus: 'These six external bases are impermanent.'"

Nandaka: "Good, good, sisters! So it is with a noble disciple who sees this as it actually is with proper wisdom. Sisters, what do you think? Is eye-consciousness....ear consciousness...nose-consciousness... tongue-consciousness... body-consciousness... mind-consciousness permanent or impermanent?"
Bhikkunis: "Impermanent, venerable sir."
Nandaka: "Is what is impermanent suffering or happiness?"
Bhikkunis: "Suffering, venerable sir."
Nandaka: "Is what is impermanent, suffering, and subject to change fit to be regarded thus: 'This is mine, this I am, this is my self'?"
Bhikkunis: "No, venerable sir. Why is that? Because, venerable sir, we have already seen this well as it actually is with proper wisdom thus: 'These six classes of consciousness are impermanent.'" 
Nandaka: ​"Good, good, sisters! So it is with a noble disciple who sees this as it actually is with proper wisdom. Sisters, suppose an oil-lamp is burning: its oil is impermanent and subject to change, its wick is impermanent and subject to change, its flame is impermanent and subject to change, and its radiance is impermanent and subject to change. Now would anyone be speaking rightly who spoke thus: 'While this oil-lamp is burning, its oil, wick, and flame are impermanent and subject to change, but its radiance is permanent, everlasting, eternal, not subject to change'?"
Bhikkunis: "No, venerable sir. Why is that? Because, venerable sir, while that oil-lamp is burning, its oil, wick, and flame are impermanent and subject to change, so its radiance must be impermanent and subject to change."

Nandaka: "So too, sisters, would anyone be speaking rightly who spoke thus: 'These six internal bases are impermanent and subject to change, but the pleasant, painful, or neither-painful-nor-pleasant feeling that one experiences in dependence upon the six internal bases is permanent, everlasting, eternal, not subject to change'?" Bhikkunis: "No, venerable sir. Why is that? Because each feeling arises in dependence upon its corresponding condition and with the cessation of its corresponding condition, the feeling ceases."

Nandaka : "Good, good, sisters! So it is with a noble disciple who sees this as it actually is with proper wisdom. Sisters, suppose a great tree is standing possessed of heartwood: its root is impermanent and subject to change, its trunk is impermanent and subject to change, its branches and foliage are impermanent and subject to change, and its shadow is impermanent and subject to change. Now would anyone be speaking rightly who spoke thus: 'The root, trunk, branches, and foliage of this great tree standing possessed of heartwood are impermanent and subject to change, but its shadow is permanent, everlasting, eternal, not subject to change'?"
Bhikkunis: "No, venerable sir. Why is that? Because, venerable sir, the root, trunk, branches, and foliage of this great tree standing possessed of heartwood are impermanent and subject to change, so its shadow must be impermanent and subject to change."
Nandaka: "So too, sisters, would anyone be speaking rightly who spoke thus: 'These six external bases are impermanent and subject to change, but the pleasant, painful, or neither-painful-nor-pleasant feeling that one experiences in dependence upon the six external bases is permanent, everlasting, eternal, not subject to change'?"

Bhikkunis: "No, venerable sir. Why is that? Because each feeling arises in dependence upon its corresponding condition, and with the cessation of its corresponding condition, the feeling ceases."
Nandaka: "Good, good, sisters! So it is with a noble disciple who sees this as it actually is with proper wisdom. Sisters, suppose a skilled butcher or his apprentice were to kill a cow and carve it up with a sharp butcher's knife. Without damaging the inner mass of flesh and without damaging the outer hide, he would cut, sever, and carve away the inner tendons, sinews, and ligaments with the sharp butcher's knife. Then having cut all this away, he would remove the outer hide and cover the cow again with that same hide. Would he be speaking rightly if he were to say: 'This cow is joined to this hide just as it was before'?"
Bhikkunis: "No, venerable sir. Why is that? Because if that skilled butcher or his apprentice were to kill a cow...and cut and carve all that away, even though he covers the cow again with that same hide and says: 'This cow is joined to this hide just as it was before,' that cow would still be disjoined from that hide."

Nandaka: "Sisters, I have given this simile in order to convey a meaning. This is the meaning: 'The inner mass of flesh' is a term for the six internal bases. "The outer hide' is a term for the six external bases. 'The inner tendons, sinews, and ligaments' is a term for delight and lust. 'The sharp butcher's knife' is a term for noble wisdom - the noble wisdom that cuts, severs, and carves away the inner defilements, fetters, and bonds. "

"Sisters, there are these seven enlightenment factors through the development and cultivation of which a bhikkhu, by realizing for himself with direct knowledge, here and now enters upon and abides in the deliverance of mind and deliverance by wisdom that are taintless with the destruction of the taints. What are the seven? Here, sisters, a bhikkhu develops the mindfulness enlightenment factor, which is supported by seclusion, dispassion, and cessation, and ripens in relinquishment. He develops the investigation-of-states enlightenment factor. . .the energy enlightenment factor.. .the rapture enlightenment factor...the tranquility enlightenment factor...the concentration enlightenment factor...the equanimity enlightenment factor, which is supported by seclusion, dispassion, and cessation, and ripens in relinquishment. These are the seven enlightenment factors through the development and cultivation of which a bhikkhu, by realizing for himself with direct knowledge, here and now enters upon and abides in the deliverance of mind and deliverance by wisdom that are taintless with the destruction of the taints." 
​When the venerable Nandaka had advised the bhikkhunis thus, he dismissed them, saying: "Go, sisters, it is time." Then the bhikkhunis, having delighted and rejoiced in the venerable Nandaka's words, rose from their seats, and after paying homage to the venerable Nandaka, departed keeping him on their right. They went to the Blessed One, and after paying homage to him, stood at one side.

The Blessed One told them: "Go, sisters, it is time." Then the bhikkhunis paid homage to the Blessed One and departed keeping him on their right. Soon after they had left, the Blessed One addressed the bhikkhus: "Bhikkhus, just as on the Uposatha day of the fourteenth people are not doubtful or perplexed as to whether the moon is incomplete or full, since then the moon is clearly incomplete, so too, those bhikkhunis are satisfied with Nandaka's teaching of the Dhamma, but their intention has not yet been fulfilled."

Then the Blessed One addressed the venerable Nandaka: "Well then, Nandaka, tomorrow too you should advise those bhikkhunis in exactly the same way." "Yes, venerable sir," the venerable Nandaka replied.

Then, the next morning, the venerable Nandaka dressed...and went to the bhikkunis...Then the bhikkhunis paid homage to the Blessed One and departed keeping him on their right. Soon after they had left, the Blessed One addressed the bhikkhus: "Bhikkhus, just as on the Uposatha day of the fifteenth people are not doubtful or perplexed as to whether the moon is incomplete or full, since then the moon is clearly full, so too, those bhikkhunis are satisfied with Nandaka's teaching of the Dhamma and their intention has been fulfilled. Bhikkhus, even the least advanced of those five hundred bhikkhunis is a stream-enterer, no longer subject to perdition, bound [for deliverance], headed for enlightenment."

That is what the Blessed One said. The bhikkhus were satisfied and delighted in the Blessed One's words. 
In summary, Venerable Nandaka was instructed by the Buddha to give the nuns (Mahapajapati Gotami's followers) a discourse. He taught them on impermanence (anicca) and what is impermanent will cause suffering (dukkha). He also taught them the seven enlightenment factors  through the development and cultivation of which a bhikkhu, by realizing for himself with direct knowledge, here and now enters upon and abides in the deliverance of mind and deliverance by wisdom that are taintless with the destruction of the taints. At the end of the teaching, even the least advanced nun attain the stream entry stage of enlightenment. 
References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The middle length discourses of the Buddha (Bhikkhu Bodhi)