It is narrated from Anas that the Messenger of Allah (ص) said:
"The Lord of the Worlds entrusted me with a covenant about Ali ibn Abi Talib and said: He is the banner of guidance, the beacon of faith and the Imam of my friends and followers. He is the radiance for all those who obey me.
O Abu Barzah, Ali ibn Abi Talib will be my confidant on the Resurrection Day and he would be the holder of my flag on the Resurrection and the bearer of the keys to the treasures of my Lord’s Mercy."
[1] In Tarikh-e-Baghdad, the word Paradise has come down instead of Mercy.
[2] Abu Na'im Esfahani, Hilyatul Auliya, V.1, page 66; Kharazmi, Al-Manaqib, page 311-312; Khatib Baghdadi, Tarikh-e-Baghdad, V.14, page 102; Tarikh Madinah-Damishq, V.42, page 330; Qunduzi, Yanabi al-Muwadda, V.1, page 233-234, V.2, page 485. Also, refer to Aini, Manaqib Sayedna Ali, page 62.