Al-Muwatta Hadith 29.71

Yahya related to me from Malik from Ibn Shihab that Said ibn al-Musayyab said, "The idda of the woman who bleeds constantly is a year." Malik said, "What is done among us about a divorced woman whose periods stop when her husband divorces her is that she waits nine months. If she has not had a period in them, she has an idda of three months. If she has a period before the end of the three months, she accepts the period. If another nine months pass without her having a period, she does an idda of three months. If she has a second period before the end of those three months, she accepts the period. If nine months then pass without a period, she does an idda of three months. If she has a third period, the idda of the period is complete. If she does not have a period, she waits three months, and then she is free to marry. Her husband can return to her before she becomes free to marry unless he made her divorce irrevocable." Malik said, "The sunna with us is that when a man divorces his wife and has the option to return to her, and she does part of her idda and then he returns to her and then parts from her before he has had intercourse with her, she does not add to what has passed of her idda. Her husband has wronged himself and erred if he returned to her and had no need of her." Malik said, "What is done among us is that if a woman becomes a muslim while her husband is a kafir and then he becomes muslim, he is entitled to her as long as she is in her idda. If her idda is finished, he has no access to her. If he remarries her after the end of her idda, however, that is not counted as divorce. Islam removed her from him without divorce."