Shaykh Imam al-Bayhaqi (may Allah have mercy on him) said: Abu Ma'bad Hafs bin Ghaylan narrated it from Sulayman bin Musa with his chain up to Amr bin al-As (may Allah be pleased with him): The 'iddah of an umm walad, when her master dies, is four months and ten days, and when she is set free, her 'iddah is three menstrual periods.
Abu Abd al-Rahman al-Sulami and Abu Bakr bin al-Harith (may Allah have mercy on them both) informed us; they said: Ali bin Umar al-Hafiz (may Allah have mercy on him) informed us; Muhammad bin al-Hasan bin Ali al-Yaqtini narrated to us; al-Husayn bin Abdullah bin Yazid al-Qattan narrated to us; Abbas bin al-Walid al-Khallal al-Dimashqi narrated to us; Zayd bin Yahya bin Ubayd narrated to us; he said: Abu Ma'bad narrated to us, and he mentioned it. Ali (bin Umar al-Daraqutni) said: It is mawquf, and that is correct, and it is mursal, because Qabisah did not hear from Amr bin al-As (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15583