Sahih Muslim | Book 23 | Hadith Number 5044

Narrated by Jabir
Jabir reported Allah's Messenger (may peace be upon him) as saying: When any one of you drops a mouthful he should pick it up and remove any of the filth on it, and then eat it, and should not leave it for the Satan, and should not wipe his hand with towel until he has licked his fingers, for he does not know in what portion of the food the blessing lies.