Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: A maidservant of the household of the Prophet (peace and blessings be upon him) committed a sin (of fornication), so the Prophet (peace and blessings be upon him) said: "O Ali, carry out the prescribed punishment on her." The narrator says: Sayyiduna Ali (may Allah be pleased with him) left her until she had given birth to the child in her womb. Then Sayyiduna Ali (may Allah be pleased with him) gave her fifty lashes. Then he came to the Prophet (peace and blessings be upon him) and mentioned this to him, and he said: "You have done right."
Abu Ya'la recorded it. Its chain contains Mandal bin Ali, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الحدود والديات / 10514