Musannaf Ibn Abi Shayba 16:279

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from al-Jurayri, from Abu al-Ward, from Ibn A’bad (or Ibn Ma’bad), who said: Ali said: "Do you know what the right of food is?" I said: "And what is its right?" He said: "You say: 'In the name of Allah, O Allah, bless for us that which You have provided for us.'" Then he said: "Do you know what its gratitude is?" I said: "And what is its gratitude?" He said: "You say: 'Praise be to Allah who fed us and gave us drink.'"