Sunan Abi Dawud Book 28, Hadith 110
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 a fly alights in anyone’s vessel, he should plunge it all in, for in one of its wings there is a disease, and in the other is a cure. It prevents the wing of it is which there is a cure, so plunge it all in (the vessel).
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.