Hadith 1, 40 Hadith Qudsi
On the authority of Abu Hurayrah (may Allah be pleased with him), who said that the Messenger of Allah (ﷺ) 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-Nasa'i and Ibn Majah).
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" 
رواه مسلم (وكذلك البخاري والنسائي وابن ماجه)