Muwatta Malik 1231

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 ‏.‏

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

Reference

Muwatta Malik 1231

In-book

Book 29, Hadith 28