Then a number of bhikkhus approached the Blessed One … and said to him: sn.iv.51 “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.”
“For sure, 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.
“But, bhikkhus, if wanderers of other sects ask you: ‘What, friends, is that suffering for the full understanding of which the holy life is lived under the ascetic Gotama?’—being asked thus, you should answer them thus: ‘The eye, friends, is suffering: it is for the full understanding of this that the holy life is lived under the Blessed One. Forms are suffering … Whatever feeling arises with eye-contact as condition … that too is suffering … The mind is suffering … Whatever feeling arises with mind-contact as condition … that too is suffering: it is for the full understanding of this that the holy life is lived under the Blessed One. This, friends, is that suffering for the full understanding of which the holy life is lived under the Blessed One.’ sn.iv.52
“Being asked thus, bhikkhus, you should answer those wanderers of other sects in such a way.”