وَعَنْ أَبِي هُرَيْرَةَ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«مَنْ نَسِيَ وَهُوَ صَائِمٌ، فَأَكَلَ أَوْ شَرِبَ، فَلْيُتِمَّ صَوْمَهُ، فَإِنَّمَا أَطْعَمَهُ اَللَّهُ وَسَقَاهُ»
‘Whoever forgets that he is fasting, and eats or drinks is to complete his fast, as it was Allah who fed him and gave him something to drink.’ Agreed upon.
Bulugh al-Maram 777, Book 5, Fasting, Hadith 20. 1 min read