Abdullah bin Utbah (may Allah have mercy on him) narrates from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that a slave may marry two women and gives two divorces, and a slave-woman observes a waiting period of two menstrual cycles; if she does not menstruate, then two months, or a month and a half.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13895