It is narrated from Amr bin al-As (may Allah be pleased with him): Do not confuse the Sunnah of our Prophet (peace and blessings be upon him) for us. The 'iddah of an umm walad is like the 'iddah of a woman whose husband has died: four months and ten days. In the narration of Yazid: The 'iddah of an umm walad is four months and ten days.
Abu Bakr bin al-Harith al-Faqih said that Abu al-Hasan al-Daraqutni al-Hafiz said: Qabisah did not hear from Amr, and the correct wording is: Do not confuse our religion for us. (It is mawquf.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15580