Sahih al-Bukhari 4529
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · "And when you have divorced women and they have fulfilled the term of their prescribed period, do not prevent them from marrying their (former) husbands..." (V.2:232)
Narrated Al-Hasan:
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ ، حَدَّثَنَا أَبُو عَامِرٍ الْعَقَدِيُّ ، حَدَّثَنَا عَبَّادُ بْنُ رَاشِدٍ ، حَدَّثَنَا الْحَسَنُ ، قَالَ حَدَّثَنِي مَعْقِلُ بْنُ يَسَارٍ ، قَالَ كَانَتْ لِي أُخْتٌ تُخْطَبُ إِلَىَّ. وَقَالَ إِبْرَاهِيمُ عَنْ يُونُسَ ، عَنِ الْحَسَنِ ، حَدَّثَنِي مَعْقِلُ بْنُ يَسَارٍ ،. حَدَّثَنَا أَبُو مَعْمَرٍ ، حَدَّثَنَا عَبْدُ الْوَارِثِ ، حَدَّثَنَا يُونُسُ ، عَنِ الْحَسَنِ ، أَنَّ أُخْتَ، مَعْقِلِ بْنِ يَسَارٍ طَلَّقَهَا زَوْجُهَا، فَتَرَكَهَا حَتَّى انْقَضَتْ عِدَّتُهَا، فَخَطَبَهَا فَأَبَى مَعْقِلٌ، فَنَزَلَتْ {فَلاَ تَعْضُلُوهُنَّ أَنْ يَنْكِحْنَ أَزْوَاجَهُنَّ} .
The sister of Ma'qal bin Yasar was divorced by her husband who left her till she had fulfilled her term of 'Iddat (i.e. the period which should elapse before she can Remarry) and then he wanted to remarry her but Maqal refused, so this Verse was revealed:-- "Do not prevent them from marrying their (former) husbands." (2.232)