Hadith 514990
Chapter 40: The Mudabbar - كتاب المدبر
حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، دَبَّرَ جَارِيَتَيْنِ لَهُ فَكَانَ يَطَؤُهُمَا وَهُمَا مُدَبَّرَتَانِ .
Malik related to me from Nafi that Abdullah ibn Umar made two of his slave-girls mudabbara, and he had intercourse with them while they were mudabbara.
Reference Muwatta Malik 514990
USC-MSA web (English) reference : Book 40, Hadith 4