Full Sharh — Riyad as-Salihin 72
وعنه أن رسول الله صلى الله عليه وسلم قال: "إن الشيطان يحضر أحدكم عند كل شئ من شأنه، حتى يحضره عند طعامه؛ فإذا سقطت لقمة أحدكم فليأخذها فليمط ما كان بها من أذى، ثم ليأكلها ولا يدعها للشيطان، فإذا فرغ فليلعق أصابعه؛ فإنه لا يدرى في أي طعامه البركة".((رواه مسلم))
English Translation
Jabir (May Allah be pleased with him) reported:: The Messenger of Allah (ﷺ) said, "Satan appears at every thing done by you; he appears even at one's dinner. When a morsel of any of you falls, he should pick it up and remove any dirt on it, and then eat it. He should not leave it for Satan, nor should he wipe his hand with the towel until he has licked his fingers, for he does not know in what portion of the food the blessing lies.".
Source
Riyad as-Salihin(رياض الصالحين)
The Book About the Etiquette of Eating
Hadith Number
72