The 1st of the 40 hadiths gathered by Various compilers in Forty Hadith Qudsi, given below in the original Arabic with an English translation and its reference.
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)
Text from the open hadith-api dataset. Hadith numbering follows that edition and can differ slightly from a printed copy — check the Arabic against a trusted mushaf of hadith before relying on a reference.