Muwatta Imam Malik Book of Divorce, Hadith 73

Yahya related to me from Malik that he had heard that Umar ibn al-Khattab, Abdullah ibn Umar, Abdullah ibn Masud, Salim ibn Abdullah, al-Qasim ibn Muhammad, Ibn Shihab,and Sulayman ibn Yasar all said, "If a man has vowed to divorce his wife before marrying her and then he breaks his vow, divorce is obligatory for him when he marries her."

وَحَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عُمَرَ بْنَ الْخَطَّابِ، وَعَبْدَ اللَّهِ بْنَ عُمَرَ، وَعَبْدَ اللَّهِ بْنَ مَسْعُودٍ، وَسَالِمَ بْنَ عَبْدِ اللَّهِ، وَالْقَاسِمَ بْنَ مُحَمَّدٍ، وَابْنَ، شِهَابٍ وَسُلَيْمَانَ بْنَ يَسَارٍ كَانُوا يَقُولُونَ إِذَا حَلَفَ الرَّجُلُ بِطَلاَقِ الْمَرْأَةِ قَبْلَ أَنْ يَنْكِحَهَا ثُمَّ أَثِمَ إِنَّ ذَلِكَ لاَزِمٌ لَهُ إِذَا نَكَحَهَا .