R. Alexandri said: R. Joshua b. Levi pointed out a contradiction. It is written, in its time [will the Messiah come], whilst it is also written, [the Lord] will hasten it!" – If they are worthy, I will hasten it: if not, [he will come] at the due time.

R. Alexandri said: R. Joshua opposed two verses: it is written. And behold, one like the son of man came with the clouds of heaven; whilst [elsewhere] it is written, [behold, thy king cometh unto thee. . .] lowly, and riding upon an ass!' - If they are meritorious, [he will come] with the clouds of heaven; if not, lowly and riding upon an ass.

The disciples of R. Jose b. Kisma asked him, 'When will the Messiah come?' -He answered, 'I fear lest ye demand a sign of me [that my answer is correct].' They assured him, 'We will demand no sign of you.' So he answered them, 'When this gate' falls down, is rebuilt, falls again, and is again rebuilt, and then falls a third time, before it can be rebuilt the son of David will come.' They said to him, 'Master, give us a sign.' He protested, 'Did ye not assure me that ye would not demand a sign?' They replied, 'Even so, [we desire one].' He said to them. 'If so, let the waters of the grotto of Paneas turn into blood;' and they turned into blood. When he lay dying he said to them, 'Place my coffin deep [in the earth], '

Source: Babylonian Talmud, Tractate Sanhedrin 98a-98b