Muwatta Malik 1207

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ إِذَا طَلَّقَ الْعَبْدُ امْرَأَتَهُ تَطْلِيقَتَيْنِ فَقَدْ حَرُمَتْ عَلَيْهِ حَتَّى تَنْكِحَ زَوْجًا غَيْرَهُ حُرَّةً كَانَتْ أَوْ أَمَةً وَعِدَّةُ الْحُرَّةِ ثَلاَثُ حِيَضٍ وَعِدَّةُ الأَمَةِ حَيْضَتَانِ ‏.‏

Yahya related to me from Malik from Nafi that Abdullah ibn Umar said, "When the slave divorces his wife twice, she is haram for him until she has married another husband, whether she is free or a slave. The idda of a free woman is three menstrual periods, and the idda of a slave-girl is two periods

Reference

Muwatta Malik 1207

In-book

Book 29, Hadith 4