Kimatthiya Sutta SN 45.5
At Savatthī. Then a number of bhikkhus approached the Blessed One…. Sitting to one side, those bhikkhus said to the Blessed One:
“Here, venerable sir, wanderers of other sects ask us: ‘For what purpose, friends, is the holy life lived under the ascetic Gotama?’ When we are asked thus, venerable sir, we answer those wanderers thus: ‘It is, friends, for the full understanding of suffering that the holy life is lived under the Blessed One.’ We hope, venerable sir, that when we answer thus we state what has been said by the Blessed One and do not misrepresent him with what is contrary to fact; that we explain in accordance with the Dhamma, and that no reasonable consequence of our assertion gives ground for criticism.”
“Surely, bhikkhus, when you answer thus you state what has been said by me and do not misrepresent me with what is contrary to fact; you explain in accordance with the Dhamma, and no reasonable consequence of your assertion gives ground for criticism. For, bhikkhus, it is for the full understanding of suffering that the holy life is lived under me.
“If, bhikkhus, wanderers of other sects ask you: ‘But, friends, is there a path, is there a way for the full understanding of this suffering? ’—being asked thus, you should answer them thus: ‘There is a path, friends, there is a way for the full understanding of this suffering.’
“And what, bhikkhus, is that path, what is that way for the full understanding of this suffering? It is this Noble Eightfold Path; that is, right view … right concentration. This is the path, this is the way for the full understanding of this suffering.
“Being asked thus, bhikkhus, you should answer those wanderers of other sects in such a way.”
Source: Kimatthiya Sutta SN 45.5 SN v 6