Sayyidina Anas reported that when the Prophet (SAW) finished eating, he would lick his three fingers. He would say, “If a morsel of one of you falls down then he must clean it remove the inj’urous, and eat it and leave it not for the devil.” He commanded us to lick the plate clean, saying, “You cannot imagine in which portion of your meal lies blessing.”
[Ahmed 12815, Muslim 2034, Abu Dawud 3845]