It is narrated from Amr bin Aws (may Allah be pleased with him) that Umar (may Allah be pleased with him) said: If only I were able to make the waiting period of a slave woman one and a half menstrual cycles, I would have done so. A man said: O Commander of the Believers, make it a month and a half. Then Umar (may Allah be pleased with him) remained silent.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15454