Musnad Ahmad 33:514

Abdullah ibn al-Walid, who is called al-Adani, narrated to us, Sufyan narrated to us, from Abu al-Zubayr, from Jabir, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "If a morsel of food of one of you falls, let him remove whatever harm is upon it, then let him eat it, and let him not leave it for the Shaytan. And let not one of you wipe his hand with a cloth until he licks his fingers or has them licked, for he does not know in which part of his food the blessing lies."