Messenger of Allah (ﷺ) commanded the licking of fingers (after eating) and the cleaning of the dish, saying: "You do not know in what portion the Blessing (of Allah) lies".

[Muslim].

In another narration, Jabir said: Messenger of Allah (ﷺ) said, "When a morsel of any of you falls down, you should pick it up and remove any dirt or dust on it and then eat it; and don't leave it for Satan; and do not wipe your hand with the towel until you have licked your fingers, for you do not know in what portion of the food the Barakah* (of Allah) lies".

* Barakah is the Abundance of goodness and its continuity.