"When the Prophet (ﷺ) ate, he would lick his three fingers, and he said: 'If one of you drops a piece (of food) then let him remove any harm (dirt) from it and eat it, and do not leave it for Ash-Shaitan.' And he would order us to finish (clean) the dish. And he said: 'Indeed you do not know in which part of your food is the blessing.' [Abu 'Eisa said:] This Hadith is Hasan Gharib Sahih.
حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ الْخَلاَّلُ، حَدَّثَنَا عَفَّانُ بْنُ مُسْلِمٍ، حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، حَدَّثَنَا ثَابِتٌ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ إِذَا مَا أَكَلَ طَعَامًا لَعِقَ أَصَابِعَهُ الثَّلاَثَ وَقَالَ " إِذَا مَا وَقَعَتْ لُقْمَةُ أَحَدِكُمْ فَلْيُمِطْ عَنْهَا الأَذَى وَلْيَأْكُلْهَا وَلاَ يَدَعْهَا لِلشَّيْطَانِ " . وَأَمَرَنَا أَنْ نَسْلُتَ الصَّحْفَةَ وَقَالَ " إِنَّكُمْ لاَ تَدْرُونَ فِي أَىِّ طَعَامِكُمُ الْبَرَكَةُ " . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ .
Tirmizi
The Book on Food • Hadith 1863