Abul Hasan Mohammad bin Jaafar Al-Nahwy narrated from his father, from Mohammad bin Hasan bin ALI Al-Qazwiny, from Ahmad bin Dawud, from Mohammad bin Saleh, from Abbas bin Rabee’, from ‘Esma bin Ismail, from Abu Ma'shar, from Abu Huraira, who said:
The MESSENGER OF ALLAH (SWT) said:
On the night of Me’raaj, I heard a call from under the Throne that said, “ALI (ASWS) is the sign of guidance and he is the heir of My love (the PROPHET (SAWW)), so announce it.”
When I came down from the heavens, ALLAH (SWT) reminded me of this incident through the revelation of this verse, " O Messenger, deliver what has been sent down to you from your Lord. And if you do not do it (it will be as if) you have not delivered His message (at all)" (5:67).
(Ref : Ghayatol Maram Page 207 Hadees No. 13)