Musnad Ahmad 33:999

Rawh narrated to us, Ibn Jurayj narrated to us, Abu al-Zubayr informed me that he heard Jabir ibn Abdullah saying: "For every prophet, there is a supplication with which he has supplicated for his nation, and I have hidden my supplication as an intercession for my nation on the Day of Resurrection." Meaning the Prophet, may God bless him and grant him peace.