From K.R. Norman's translation of Sn 5.7, lines 1075-1076:
1075. 'He who has gone out, does he not exist, or does he remain unimpaired for ever? Explain this to me well, sage, for thus is this doctrine known to you.'
1076. 'There is no measuring of one who has gone out, Upasīva,' said the Blessed One. 'That no longer exists for him by which they might speak of him. When all phenomena have been removed, then all ways of speaking are also removed.'
Ven. Thanissaro's translation of the same:
[Upasiva:]
He who has reached the end: Does he not exist, or is he for eternity free from dis-ease? Please, sage, declare this to me as this phenomenon has been known by you.
[The Buddha:]
One who has reached the end has no criterion [3] by which anyone would say that — for him it doesn't exist. When all phenomena are done away with,[4] all means of speaking are done away with as well.
3.
For a discussion of the meaning of "criterion" in this passage, see The Mind Like Fire Unbound, Chapter 1.
4.
Although Upasiva refers to the goal as a phenomenon (dhamma), the Buddha describes it as the transcending of all phenomena. For some of the implications of this statement, see AN 3.134.
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I think Wittgenstein's famous quote sums up how the Buddha is teaching us to regard the question.
Ludwig Wittgenstein wrote:Whereof one cannot speak, thereof one must be silent.