Musnad Abu Ya'la al-Mawsili 115:129

Abu Khaythama narrated to us, Yahya narrated to us, from Shu'bah, Qatada narrated to us, from Anas, from the Prophet (may Allah bless him and grant him peace), who said: "Indeed, for every prophet there is a supplication with which he supplicated for his nation, and I have reserved my supplication as an intercession for my nation."