Muwatta Malik 1121

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي عَبْدِ الرَّحْمَنِ، عَنْ زَيْدِ بْنِ ثَابِتٍ، أَنَّهُ كَانَ يَقُولُ فِي الرَّجُلِ يُطَلِّقُ الأَمَةَ ثَلاَثًا ثُمَّ يَشْتَرِيهَا إِنَّهَا لاَ تَحِلُّ لَهُ حَتَّى تَنْكِحَ زَوْجًا غَيْرَهُ ‏.‏

Yahya related to me from Malik from Ibn Shihab from Abu Abd ar- Rahman that Zayd ibn Thabit said that if a man divorced his slave-girl three times and then bought her, she was not halal for him until she had married another husband

Reference

Muwatta Malik 1121

In-book

Book 28, Hadith 31