عَنْ أَبِي هُرَيْرَةَ
قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَمَّا قَضَى اللَّهُ الْخَلْقَ، كَتَبَ فِي كِتَابِهِ عَلَى نَفْسِهِ، فَهُوَ مَوْضُوعٌ عِنْدَهُ: إِنَّ رَحْمَتِي تَغْلِبُ غَضَبِي»
The Messenger of Allah (sallallahu alayhi wa sallam) said: When Allah decreed the Creation He pledged Himself by writing in His book which is laid down with Him: My mercy prevails over my wrath. It was related by Muslim (also by al-Bukhari, an-Nasai and Ibn Majah).
The Forty Qudsi 1, Book 1, Forty Hadith Qudsi, Hadith 1. 1 min read