Hadith 511580
Chapter 29: Divorce - كتاب الطلاق
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ، كَانَ يَقُولُ فِي الرَّجُلِ يَقُولُ لاِمْرَأَتِهِ أَنْتِ عَلَىَّ حَرَامٌ إِنَّهَا ثَلاَثُ تَطْلِيقَاتٍ . قَالَ مَالِكُ وَذَلِكَ أَحْسَنُ مَا سَمِعْتُ فِي ذَلِكَ .
Yahya related to me from Malik that he had heard that Ali ibn Abi Talib used to say that if a man said to his wife, "You are haram for me," it counted as three pronouncements of divorce. Malik said, "That is the best of what I have heard on the subject."
Reference Muwatta Malik 511580
USC-MSA web (English) reference : Book 29, Hadith 6