Muwatta Malik 1205

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ نُفَيْعًا، مُكَاتَبًا كَانَ لأُمِّ سَلَمَةَ زَوْجِ النَّبِيِّ صلى الله عليه وسلم طَلَّقَ امْرَأَةً حُرَّةً تَطْلِيقَتَيْنِ فَاسْتَفْتَى عُثْمَانَ بْنَ عَفَّانَ فَقَالَ حَرُمَتْ عَلَيْكَ ‏.‏

Yahya related to me from Malik from Ibn Shihab from Said ibn al- Musayyab that Nufay, a mukatab of Umm Salama, the wife of the Prophet, may Allah bless him and grant him peace, divorced his free wife twice, so he asked Uthman ibn Affan for an opinion, and he said, "She is haram for you

Reference

Muwatta Malik 1205

In-book

Book 29, Hadith 2