Anas reported that when Allah's Messenger (ﷺ) ate food he licked his three fingers, and he said: When any one of you drops a mouthful he should remove anything filthy from it and then eat it, and should not leave it for the Satan. He also commanded us that we should wipe the dish saying: You do not know in what portion of your food the blessing lies.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ، وَأَبُو بَكْرِ بْنُ نَافِعٍ الْعَبْدِيُّ قَالاَ حَدَّثَنَا بَهْزٌ، حَدَّثَنَا حَمَّادُ، بْنُ سَلَمَةَ حَدَّثَنَا ثَابِتٌ، عَنْ أَنَسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا أَكَلَ طَعَامًا لَعِقَ أَصَابِعَهُ الثَّلاَثَ . قَالَ وَقَالَ " إِذَا سَقَطَتْ لُقْمَةُ أَحَدِكُمْ فَلْيُمِطْ عَنْهَا الأَذَى وَلْيَأْكُلْهَا وَلاَ يَدَعْهَا لِلشَّيْطَانِ " . وَأَمَرَنَا أَنْ نَسْلُتَ الْقَصْعَةَ قَالَ " فَإِنَّكُمْ لاَ تَدْرُونَ فِي أَىِّ طَعَامِكُمُ الْبَرَكَةُ " .
sunnah.com