Yahya related to me from Malik from Nafi that Abdullah ibn Umardivorced his wife while she was menstruating in the time of theMessenger of Allah, may Allah bless him and grant him peace, Umar ibnal-Khattab asked the Messenger of Allah, may Allah bless him and granthim peace, about it. The Messenger of Allah, may Allah bless him andgrant him peace, said, "Go and tell him to take her back and keep heruntil she is purified and then has a period and then is purified. Thenif he wishes, he an keep her, and if he wishes he should divorce herbefore he has intercourse with her. That is the idda which Allah hascommanded for women who are divorced."
USC-MSA web (English) reference: Book 29, Hadith 53
Arabic reference: Book 29, Hadith 1214