Sayyiduna Abu Hurairah, may Allah be pleased with him, narrates this statement of the Prophet Muhammad, peace and blessings be upon him: "When a fasting person forgetfully eats something or forgetfully drinks something, he should complete his fast, for it is Allah Almighty who has fed him and given him drink."
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3519
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الإرواء» (4/ 86 / 938): ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطNull