Musannaf Ibn Abi Shayba 32:1

Abu Khalid al-Ahmar narrated to us, from Ibn ‘Ajlan, from his father, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When Allah created the creation, He wrote with His Hand upon Himself: 'Indeed, My mercy overcomes My wrath.'"