When any one of you drops a mouthful he should pick it up and remove any of the filth on it, and then eat it, and should not leave it for the Satan, and should not wipe his hand with towel until he has licked his fingers, for he does not know in what portion of the food the blessing lies. (Using translation from Muslim 2033b)   

قَالَ رَسُولُ اللهِ ﷺ «إِذَا سَقَطَتْ مِنْ أَحَدِكُمْ لُقْمَةٌ فَلْيُمِطْ مَا أَصَابَهَا مِنْ أَذًى فَلْيَأْكُلْهَا وَلَا يَدَعْهَا لِلشَّيْطَانِ وَلَا يَمْسَحْ يَدَهُ بِالْمِنْدِيلِ حَتَّى يَلْعَقَهَا أَوْ يُلْعِقَهَا فَإِنَّهُ لَا يَدْرِي فِي أَيِّ طَعَامِهِ الْبَرَكَةُ»