Sahih al-Bukhari 6669
Sahih al-Bukhari · Book 83: Oaths and Vows · If someone does something against his oath due to forgetfulness
Narrated Abu Huraira:
حَدَّثَنِي يُوسُفُ بْنُ مُوسَى ، حَدَّثَنَا أَبُو أُسَامَةَ ، قَالَ حَدَّثَنِي عَوْفٌ ، عَنْ خِلاَسٍ ، وَمُحَمَّدٍ ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم " مَنْ أَكَلَ نَاسِيًا وَهْوَ صَائِمٌ فَلْيُتِمَّ صَوْمَهُ، فَإِنَّمَا أَطْعَمَهُ اللَّهُ وَسَقَاهُ " .
The Prophet (ﷺ) said, "If somebody eats something forgetfully while he is fasting, then he should complete his fast, for Allah has made him eat and drink."