Eating or drinking forgetfully — without intention to break the fast — does not break the fast and there is no qada (making up) and no kaffarah (expiation) upon the one who did so, on the authentic hadith of Abu Hurayrah: the Prophet (ﷺ) said, "Whoever forgets that he is fasting and eats or drinks, let him complete his fast — for it is Allah who has fed him and given him drink." ([al-Bukhari 6669](/hadith/bukhari/6669), Muslim 1155). The fast remains valid by the consensus of those whose disagreement is given weight. The wisdom is that the obligation in fasting is the deliberate abstention; a person cannot be held accountable for an act done in genuine forgetfulness, by the general principle: "Indeed, Allah has overlooked for my Ummah the mistake, the forgetfulness, and what they are coerced upon." (Ibn Majah 2045, sahih). However, the moment the person remembers, he must immediately stop eating or drinking; if he continues knowingly, the fast is then broken and he sins.