Sahih al-Bukhari 4614
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · Allah's Statement: "Allah will not punish you for what is unintentional in your oaths..." (V.5:89)
Narrated Aisha:
حَدَّثَنَا أَحْمَدُ بْنُ أَبِي رَجَاءٍ ، حَدَّثَنَا النَّضْرُ ، عَنْ هِشَامٍ ، قَالَ أَخْبَرَنِي أَبِي ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ أَنَّ أَبَاهَا، كَانَ لاَ يَحْنَثُ فِي يَمِينٍ حَتَّى أَنْزَلَ اللَّهُ كَفَّارَةَ الْيَمِينِ. قَالَ أَبُو بَكْرٍ لاَ أَرَى يَمِينًا أُرَى غَيْرَهَا خَيْرًا مِنْهَا، إِلاَّ قَبِلْتُ رُخْصَةَ اللَّهِ، وَفَعَلْتُ الَّذِي هُوَ خَيْرٌ.
That her father (Abu Bakr) never broke his oath till Allah revealed the order of the legal expiation for oath. Abu Bakr said, "If I ever take an oath (to do something) and later find that to do something else is better, then I accept Allah's permission and do that which is better, (and do the legal expiation for my oath ) ".