Hadith: The Messenger of Allah (may Allah’s peace and blessings be upon him) commanded licking the fingers and the dish (after eating), and he said: You do not know in which portion the blessing lies

عن جابر بن عبد الله رضي الله عنهما ، أنَّ رسول الله صلى الله عليه وسلم أمر بَلَعْقِ الأصابع والصَّحْفَةِ، وقال: «إنَّكم لا تدرون في أَيِّهَا البركة». وفي رواية: «إذا وقعت لُقْمَةُ أحدكم فليأخذها، فَلْيُمِطْ ما كان بها من أذى، وليأكلها ولا يدعها للشيطان، ولا يمسح يده بالمِنْدِيلِ حتى يَلْعَقَ أصابعه فإنه لا يدري في أَيِّ طعامه البركة». وفي رواية: «إن الشيطان يحضر أحدكم عند كل شيء من شأنه، حتى يحضره عند طعامه، فإذا سقطت من أحدكم اللُّقْمَةُ فَلْيُمِطْ ما كان بها من أذى، فليأكلها ولا يدعها للشيطان».
[صحيح] - [رواه مسلم]

Jābir ibn ‘Abdullāh (may Allah be pleased with him) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) commanded licking the fingers and the dish (after eating), and he said: "You do not know in which portion the blessing lies." In another narration, he said: "When a morsel falls from any of you, he should pick it up and remove any dirt that is on it then eat it and not leave it to the devil. He should not wipe his hand with the napkin until he has licked his fingers, for he does not know in which portion of his food the blessing lies." In a third narration, he said: "Verily, the devil is present with you in all of your affairs. He is present when your meal is brought to you. So, if a morsel fell from any of you, then he should remove any dirt that is on it then eat it and not leave it to the devil.”
Sahih/Authentic. - [Muslim]

Explanation

Jābir ibn ‘Abdullāh (may Allah be pleased with him) reported from the Prophet (may Allah's peace and blessings be upon him) some of the manners of eating, including the following: - When one finishes his meal, he should lick his fingers and wipe his plate clean until there is no trace of food on it, in order not to miss any of the blessing of the food which could be in any part of it. If a morsel of food falls on the ground, he should not leave it, because the devil accompanies the son of Adam in all of his affairs. If a morsel of food falls, the devil takes it, but we do not see him as this is a matter of the unseen world. However, we know about it through the words of our truthful Prophet (may Allah’s peace and blessings be upon him). The devil takes this fallen food and eats it, even if we still see it before us; he eats it in a manner unseen to us. This is one of the matters of the unseen that we must believe in.