Sahih Muslim Book 1, Hadith Number 388.

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”.

Amr b. Abu Sufyan reported: Abu Huraira said to Ka’b al-Ahbar that the Apostle of Allah (may peace be upon him) had said: For every apostle there Is a (special) prayer by which he would pray (to his Lord). I, however, intend (if Allah so willed) that I would reserve my prayer for the intercession of my Ummah on the Day of Resurrection. Ka’b said to Abu Huraira: Did you hear this from the Messenger of Allah (may peace be upon him)? Abu Huraira said: Yes.