Sahih Muslim Book 1, Hadith Number 392.

Chapter : Pertaining to the words of the Apostle of Allah (may peace be upon him): “I would be the first among people to Intercede in the Paradise and among the Apostles I would have the largest following”.

Anas b. Malik reported: Verily the Apostle of Allah (may peace be upon him) said: There is for every apostle a prayer with which he prays (to Allah) for his Ummah. I have reserved my prayer for the intercession of my Ummah on the Day of Resurrection.