Muwatta Malik 1468

حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ أَيُّمَا وَلِيدَةٍ وَلَدَتْ مِنْ سَيِّدِهَا فَإِنَّهُ لاَ يَبِيعُهَا وَلاَ يَهَبُهَا وَلاَ يُوَرِّثُهَا وَهُوَ يَسْتَمْتِعُ بِهَا فَإِذَا مَاتَ فَهِيَ حُرَّةٌ ‏.‏

Malik related to me from Nafi from Abdullah ibn Umar that Umar ibn al-Khattab said, "If a slave-girl gives birth to a child by her master, he must not sell her, give her away, or bequeath her. He enjoys her and when he dies she is free

Reference

Muwatta Malik 1468

In-book

Book 38, Hadith 5