Whoever forgets while fasting and eats or drinks, let him complete his fast, for it is Allah Who fed him and gave him drink
Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "Whoever forgets while fasting and eats or drinks, let him complete his fast, for it is Allah Who fed him and gave him drink."

