Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 643
Narrated Abu Huraira:
I heard Allah's Apostle saying, "Before Allah created the creations, He wrote a Book (wherein He has written): My Mercy has preceded my Anger." and that (Book) is written with Him over the Throne."