Musnad Ahmad 30:410

'Ali ibn Hafs narrated to us, Waraqa informed us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When Allah created the creation, He wrote a book, and it is with Him above the Throne: 'Verily, My mercy has preceded My wrath.'"