It is narrated from Abdullah bin Utbah that Umar bin Khattab, may Allah be pleased with him, said: "A slave may marry two women, and he will give only two divorces, and the waiting period (‘iddah) of a slave woman will be two menstrual cycles; if she does not menstruate, then the waiting period will be two or one and a half months."
Hadith Referenceمسند الإمام الشافعي / كتاب العدد والسكنى والنفقات / 1294
Hadith Takhrijصحيح: اخرجه البيهقي: 4257 - وفى المعرفة السنن والآثار له (4639) وعبد الرزاق (12872)، 13134 - والدارقطني: (3/ 308)۔
It is narrated from a man of Thaqif that he heard Umar bin Khattab (may Allah be pleased with him) saying: "If I had the power, I would make her waiting period one and a half menstruations." Upon this, a man said: "You may make her waiting period one and a half months," so Umar (may Allah be pleased with him) remained silent.
Hadith Referenceمسند الإمام الشافعي / كتاب العدد والسكنى والنفقات / 1295
Hadith Takhrijإسناده ضعيف لإبهام شيخ عمرو بن أوس - اخرجه البيهقي : 425/7 - وفي المعرفة السنن والآثار له (4640) - وعبد الرزاق (12874) وابن ابي شيبة (18768)۔
It is narrated from Nafi‘ that Ibn ‘Umar (may Allah be pleased with them) said: "An umm walad whose master passes away will observe ‘iddah for one menstrual cycle."
Hadith Referenceمسند الإمام الشافعي / كتاب العدد والسكنى والنفقات / 1296
Hadith Takhrijاسناده صحیح اخرجه البيهقي : 7 / 447 - وفى المعرفة السنن والآثار له (4693) - وعبد الرزاق (12870)، (12930) وابن ابي شيبة (18747)۔