Sunan Abi Dawud Book 28, Hadith 111
If the servant of any of you prepares food for him, and he brings it to him, while he had suffered its heat and smoke. He should make him sit with him to eat. If the food is scanty, he should put one or two morsels in his hand.
If the morsel of one of you falls down, he should wipe away anything injurious on it and eat it and not leave it for the devil. And he ordered us to clean the dish, for one of you does not leave it for the devil. And he ordered us to clean the dish, for one of you does not know in what part of his food the blessing lies.
When one of you eats, he must not wipe his hand with a handkerchief till he licks it or gives it to someone to lick.