Musnad Ahmad 132:24

Abu Abd al-Rahman narrated to us, Sa'id narrated to us, he said: Abu Marhum narrated to me, from Sahl ibn Mu'adh ibn Anas al-Juhani, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever eats food, then says: 'Praise be to Allah who fed me this and provided it to me without any power or strength from myself,' his past sins will be forgiven."