كتاب المقدمات
1
The Book of Miscellany
Abu Hurairah (May Allah be pleased with him) reported:
I heard Messenger of Allah (ﷺ) saying, "When Allah created the creatures, He wrote in the Book, which is with Him over His Throne: 'Verily, My Mercy prevailed over My Wrath"

[Al-Bukhari and Muslim].

Another narration is: Messenger of Allah (ﷺ) said, "(Allah wrote) 'My Mercy dominated My Wrath".

Still another narration is: Messenger of Allah (ﷺ) said, "(Allah wrote) 'My Mercy surpasses My Wrath".

وعن أبي هريرة، رضي الله عنه ، قال‏:‏ قال رسول الله ، صلى الله عليه وسلم لما خلق الله الخلق، كتب في كتاب، فهو عنده فوق العرش‏:‏ إن رحمتي تغلب غضبي‏"‏‏.‏
‏(‏‏(‏متفق عليه‏)‏‏)‏
Arabic/English book reference : Book 1, Hadith 419