I heard the Messenger of Allah (s.a.w.a.) say: On the night of Meraj, every time I passed by a group of angels, they asked me about Ali b. Abi Talib so often that I started to believe that Ali was more famous in the skies than I was.
When I reached the fourth sky, I saw the angel of death.
The angel of death asked me, O Mohammad, how is Ali?
I said, O my friend, how do you know Ali?
He said, O Mohammad, I am responsible for taking the life of everyone that Allah has created except for two beings, that is, your life and Alis life, because Allah himself will take your lives.
Then I reached under Arsh (the Throne) and when I looked up I saw Ali b. Abi Talib standing under the Throne of my Lord.
I said, O Ali, did you race me up here?
Then Jibraeel asked me, O Mohammad, to whom are you speaking?
I replied, I am talking to my brother, Ali b. Abi Talib.
Jibraeel replied, O Mohammad, this is not Ali. This is an angel that Allah has created in the shape of Ali b. Abi Talib. When we (angels) miss Ali b. Abi Talib, we go and look at this angel and seek forgiveness from Allah for Alis Shias.
Kanz al-Ummaal p 259 Behaar al-Anwaar v 18 p 300