بِسْمِ اللهِ الرَّحْمنِ الرَّحِيمِ
1242. Abu Hurairah (May Allah be pleased with him) reported: The Prophet (PBUH) said, "If any one of you forgetfully eats or drinks (while observing fasting) he should complete his Saum (fasting), for Allah has fed him and given him to drink.''
[Al-Bukhari and Muslim].
Commentary: This Hadith tells us of a kindness and convenience of Islam that during the Saum if a person inadvertently does any such thing which destroys his Saum, i.e., eating, drinking, etc., his Saum will remain intact due to forgetfulness, provided one abandons the act as soon as he remembers that he is observing Saum . He needs not make any expiation for such a Saum.