Sunan Abi Dawud 3845
Anas b. Malik said that when the Messenger of Allah (ﷺ) ate food, he licked his three fingers. And he said:
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.
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا حَمَّادٌ، عَنْ ثَابِتٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا أَكَلَ طَعَامًا لَعِقَ أَصَابِعَهُ الثَّلاَثَ وَقَالَ ‏"‏ إِذَا سَقَطَتْ لُقْمَةُ أَحَدِكُمْ فَلْيُمِطْ عَنْهَا الأَذَى وَلْيَأْكُلْهَا وَلاَ يَدَعْهَا لِلشَّيْطَانِ ‏"‏ ‏.‏ وَأَمَرَنَا أَنْ نَسْلُتَ الصَّحْفَةَ وَقَالَ ‏"‏ إِنَّ أَحَدَكُمْ لاَ يَدْرِي فِي أَىِّ طَعَامِهِ يُبَارَكُ لَهُ ‏"‏ ‏.‏