Harun bin Musa narrated from Jaafar bin ALI Al-Daqaaq, from Hareth bin Mohammad, from Saeed bin Katheer, from Mohammad bin Hasan, known as Shalqan, from Jaafar bin Mohammad, from his father, from Jabir bin Abdillah Al-Ansari, who said:
I heard the MESSENGER OF ALLAH (SWT) say, “The first one who enters Paradise from among the PROPHET (SAWW)s and the truthful ones is ALI BIN ABI TALEB (ASWS).”
Then Abu Dojana stood up and asked, “Did you not tell us that ALLAH (SWT) told you that Paradise is forbidden for all the PROPHET (SAWW)s before you enter it, and it is forbidden for all nations before your nation enters it?”
The PROPHET (SAWW) replied, “Yes, but do you not know that the one who carries the flag is in front of everyone? And ALI (ASWS) will be the flag bearer on the Day of Judgement who will be in front of me. He is the owner of my flag so he will enter Paradise before I do. He will lead with the flag and I will follow directly behind him.”
Then ALI (ASWS) stood up, his face beaming with joy, and said, “Praise the Lord that honoured us through you, O MESSENGER OF ALLAH (SWT).”
(Ref: Bihar Volume 7 Page 209 Hadees No.200)