It is narrated from Ibn al-Musayyab (may Allah have mercy on him) that Umar bin al-Khattab (may Allah be pleased with him) said: Any woman who is divorced and menstruates once or twice, then her menstruation stops, shall wait nine months. If a pregnancy becomes evident in her, then that is that; otherwise, after the nine months she observes a waiting period of three months, and then she becomes lawful (for marriage).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15412