Muwatta Malik, Book 4, Hadith 2 (USC-MSA) ⓘ
Yahya related to me from Malik that he had heard that the Messenger of Allah, may Allah bless him and grant him peace, said, "I forget or I am made to forget so that I may establish the sunna."
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِنِّي لأَنْسَى أَوْ أُنَسَّى لأَسُنَّ " .
also referenced under: Book 4, Hadith 224 (In-Book)