Ali (A.S)'s soul was the first to greet the Prophet (P.B.U.H&H.P)
Abu Bakr Muhammad b. Umar al-Je'abi reported from Abu Abdullah Muhammad b. al-Qasim al-Muharibi, who reports from Ismail b. Ishaq al-Rashidi, who reported from Muhammad b. al-Harith, who reported from Ibrahim b. Muhammad, from Muslim al-A'awar, from Habbah al-Arni, from Abu al-Haytham b. al-Teehan al-Ansari, who reported that:
The Prophet (P.B.U.H&H.P) said: "Allah, Most High, created the souls two thousand years earlier than the bodies attached it to the Throne and ordered them to greet me and obey me. So the first one among men who greeted me and expressed his obedience to me was the soul of Ali Ibn Abi Talib, peace be upon him."
Ref: Al Hassanain.com