Ikrimah narrates from Ibn Abbas (may Allah be pleased with them both) that when Umm Ibrahim gave birth, the Messenger of Allah (peace and blessings be upon him) said: "Her child has set her free."
Abu Bakr bin Abi Sabrah is da'if (weak) and is not used as proof, except that it has also been narrated from others from Husayn with this wording.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21782