Yahya related to me from Malik from Nafi that Abdullah ibn Umar said, "When a man divorces his wife and she begins her third period, she is free from him and he is free from her."
Malik said, "This is how things are done among us."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ كَانَ يَقُولُ إِذَا طَلَّقَ الرَّجُلُ امْرَأَتَهُ فَدَخَلَتْ فِي الدَّمِ مِنَ الْحَيْضَةِ الثَّالِثَةِ فَقَدْ بَرِئَتْ مِنْهُ وَبَرِئَ مِنْهَا . قَالَ مَالِكٌ وَهُوَ الأَمْرُ عِنْدَنَا .