Ibn Abelhadeed, the famous Sunni scholar narrated: It is narrated from Imam Ali (AS) who said: I asked the Prophet of Islam (PBUH) to request forgiveness for me from Allah (SWT).The prophet (PBUH) stood up, raised his hands towards the sky and said: O’ Allah (SWT), for the sake of the rights which Ali (AS) has with God, forgive Ali (AS). I asked the Prophet (PBUH): What kind of prayer is this? The Prophet (PBUH) replied: Is there any one more beloved than you with God so that I could call upon to intercede before Allah (SWT) [1]?
[1] Sharhe Nahjul Balaghah, Ibn Abelhadeed, Vol. 20, page 316.