Musnad Abu Ya'la al-Mawsili 160:37

Muhammad ibn Isma'il ibn Abi Samina narrated to us, Mu'tamir ibn Sulayman narrated to us, he said: I heard my father say: Qatadah narrated to us that Abu Rafi' narrated that he heard Abu Hurayrah say: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "Indeed, Allah wrote a book before He created the creation: 'Verily, My mercy has preceded My wrath.'"