Muwatta Imam Malik Book of Divorce, Hadith 17

Yahya related to me from Malik from Jafar ibn Muhammad from his father that Ali ibn Abi Talib said, "When a man takes a vow to abstain from intercourse, divorce does not occur immediately. If four months pass, he must declare his intent and either he is divorced or he revokes his vow . "
Malik said, "That is what is done among us."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، عَنْ عَلِيِّ بْنِ أَبِي طَالِبٍ، أَنَّهُ كَانَ يَقُولُ إِذَا آلَى الرَّجُلُ مِنِ امْرَأَتِهِ لَمْ يَقَعْ عَلَيْهِ طَلاَقٌ وَإِنْ مَضَتِ الأَرْبَعَةُ الأَشْهُرِ حَتَّى يُوقَفَ فَإِمَّا أَنْ يُطَلِّقَ وَإِمَّا أَنْ يَفِيءَ . قَالَ مَالِكٌ وَذَلِكَ الأَمْرُ عِنْدَنَا .