On the authority of Abu Hurayrah  (may Allāh be pleased with him) that the Prophet (صلى الله عليه وسلم)  said:

مَنْ نَسِيَ وَهُوَ صَائِمٌ، فَأَكَلَ أَوْ شَرِبَ، فَلْيُتِمَّ صَوْمَهُ، فَإِنَّمَا أَطْعَمَهُ اَللَّهُ وَسَقَاهُ – مُتَّفَقٌ عَلَيْهِ

Whoever forgets while he is fasting and he eats or drinks, let him continue (complete) his fast. Indeed it was only Allāh who fed him and gave him drink. (Agreed Upon)

The Noble Scholar Shaykh Ibn Bāz (may Allāh have mercy upon him) commented:

This is a virtue from Allāh (‘azza wa-jall). Mankind is prone to forgetfulness just as the Prophet  (صلى الله عليه وسلم) said: “I am a human being like you. I forget just as you forget.”
Forgetfulness is from human nature. Therefore if he forgets while he is fasting in Ramadan or fasting as an expiation or fasting for a reason other than these two and he eats or drinks or he has done another one of the things that breaks the fast out of forgetfulness, his fast is sound. Continue reading →