Musnad Ahmad 32:1761

'Affan narrated to us, Hammam narrated to us, Qatadah narrated to us, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "For every prophet, there is a supplication with which he supplicated and it was answered for him. And I have reserved my supplication as an intercession for my nation on the Day of Resurrection."