Sahih Muslim 2033 d
Jabir reported:
I heard Allah's Apostle (ﷺ) as saying: The Satan is present with any one of you in everything he does; he is present even when he eats food; so if any one of you drops a mouthful he should remove away anything filthy on it and eat it and not leave for the devil; and when he finishes (food) he should lick his fingers, for he does not know in what portion of his food the blessing lies.
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي سُفْيَانَ، عَنْ جَابِرٍ،
 قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏
"‏ إِنَّ الشَّيْطَانَ يَحْضُرُ أَحَدَكُمْ عِنْدَ كُلِّ شَىْءٍ
 مِنْ شَأْنِهِ حَتَّى يَحْضُرَهُ عِنْدَ طَعَامِهِ فَإِذَا سَقَطَتْ مِنْ أَحَدِكُمُ اللُّقْمَةُ فَلْيُمِطْ مَا كَانَ بِهَا مِنْ
 أَذًى ثُمَّ لْيَأْكُلْهَا وَلاَ يَدَعْهَا لِلشَّيْطَانِ فَإِذَا فَرَغَ فَلْيَلْعَقْ أَصَابِعَهُ فَإِنَّهُ لاَ يَدْرِي فِي أَىِّ طَعَامِهِ
 تَكُونُ الْبَرَكَةُ ‏"‏ ‏.‏