Imam Abu Abdullah (as) saying that Ali ibn Abu Talib (as) quite often used to say,
“We saw the Messenger of Allah (S) once in the company of al-Taymi and a friend of his while the latter was reciting Chapter al-Qadr. He (S) was profoundly moved and he kept weeping to the extent that he (S) was asked, ‘How so deeply moved by this Chapter your heart is!’
He (S) said, ‘My heart is deeply impressed because of what my eyes had witnessed, and what my mind had comprehended, and because of what the heart of this man [meaning Ali (as)] will go through after me.’
Both men asked the Messenger of Allah (S), ‘Did you really see all of that?! And what will he (Ali) see?’ He (S) would then recite the verse saying, ‘The angels and the Spirit descend therein with the permission of their Lord for every affair; peace, it is, till the break of the morn.’
Then he (S) would pause and ask them, ‘Is there anything left after the Almighty having verbally said ‘every affair’?’
They would both answer in the negative, and he (S) would then ask them, ‘Do you both know regarding whom it is revealed?’ They would both say, ‘No, by Allah, O Messenger of Allah!’
He (S) would then say, ‘Yes; is there going to be a Lailatul-Qadr after me (I.e., after my demise)?’
They would answer in the affirmative, and he (S) would then ask them, ‘Will every affair descend therein?’ They said: ‘Yes.’ He then asked them, ‘To whom will it descend?’ They answered, ‘We do not know.’
He (S), with his hand on my head, pushed me gently forward and said, ‘If you do not know, then it is regarding this person after me.’
Both men, ever since the demise of the Messenger of Allah (S), used to be filled with awe whenever that night approached.'”
Bihar al-Anwar p. 21, Vol. 94