It is narrated from Sayyiduna Ali (may Allah be pleased with him), he says: One of his slave girls committed adultery and because of that she became pregnant. I went to the Noble Prophet (peace and blessings be upon him) and informed him of this. The Prophet (peace and blessings be upon him) said: Leave her until she gives birth, then carry out the prescribed punishment on her.
Hadith Referenceالفتح الربانی / مسائل الحدود / 6720