It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that a slave may marry two wives and may give two divorces, and a slave woman observes a waiting period of two menstrual periods; if she does not menstruate, then she observes a waiting period of two months or a month and a half. Sufyan said: He is thiqah (trustworthy).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15451