When the Messenger of Allah (ﷺ) finished eating his food, he would lick his three fingers (i.e., the forefinger, the middle finger and the thumb). He (ﷺ) said, "If anyone of you drops a morsel, he should remove anything harmful from it and then eat it. He should not leave it for Shaitan." He commanded us to clean out the dish saying, "You do not know in what portion of your food the blessing lies."

[Muslim].