Qasim bin Abdur Rahman narrates from his father, who narrates from his grandfather (Sayyiduna Abdullah bin Mas'ud, may Allah be pleased with him), that the Prophet Muhammad (peace and blessings be upon him) said: "Whoever forgets to mention Allah at the beginning of his meal, then whenever he remembers, he should say: 'In the name of Allah, at its beginning and at its end.' It will be as if he has started his meal anew, and whatever harm had reached him before will be prevented."
Hadith Referenceصحیح ابن حبان / كتاب الأطعمة / 5213
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الصحيحة» (198).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح