Sahih al-Bukhari 6621
Sahih al-Bukhari · Book 83: Oaths and Vows · "Allah will not punish you for what is unintentional in your oaths, but He will punish you for your deliberate oaths ..."
Narrated `Aisha:
حَدَّثَنَا مُحَمَّدُ بْنُ مُقَاتِلٍ أَبُو الْحَسَنِ ، أَخْبَرَنَا عَبْدُ اللَّهِ ، أَخْبَرَنَا هِشَامُ بْنُ عُرْوَةَ ، عَنْ أَبِيهِ ، عَنْ عَائِشَةَ ، أَنَّ أَبَا بَكْرٍ ـ رضى الله عنه ـ لَمْ يَكُنْ يَحْنَثُ فِي يَمِينٍ قَطُّ، حَتَّى أَنْزَلَ اللَّهُ كَفَّارَةَ الْيَمِينِ وَقَالَ لاَ أَحْلِفُ عَلَى يَمِينٍ فَرَأَيْتُ غَيْرَهَا خَيْرًا مِنْهَا، إِلاَّ أَتَيْتُ الَّذِي هُوَ خَيْرٌ، وَكَفَّرْتُ عَنْ يَمِينِي.
Abu Bakr As-Siddiq had never broken his oaths till Allah revealed the expiation for the oaths. Then he said, "If I take an oath to do something and later on I find something else better than the first one, then I do what is better and make expiation for my oath."