Sahih Muslim Book - 36, Hadith - 5303

حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا جَرِيرٌ ، عَنِ الأَعْمَشِ ، عَنْ أَبِي سُفْيَانَ ، عَنْ جَابِرٍ ، قَالَ: سَمِعْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: إِنَّ الشَّيْطَانَ يَحْضُرُ أَحَدَكُمْ عِنْدَ كُلِّ شَيْءٍ مِنْ شَأْنِهِ ، حَتَّى يَحْضُرَهُ عِنْدَ طَعَامِهِ ، فَإِذَا سَقَطَتْ مِنْ أَحَدِكُمُ اللُّقْمَةُ ، فَلْيُمِطْ مَا كَانَ بِهَا مِنْ أَذًى ، ثُمَّ لِيَأْكُلْهَا ، وَلاَ يَدَعْهَا لِلشَّيْطَانِ ، فَإِذَا فَرَغَ فَلْيَلْعَقْ أَصَابِعَهُ ، فَإِنَّهُ لاَ يَدْرِي فِي أَيِّ طَعَامِهِ تَكُونُ الْبَرَكَةُ.

It was narrated that Jabir said: "I heard the Prophet (s.a.w) say: 'The Shaitan is present with any one of you in all his affairs, and he is even present with him when he eats. If one of you drops a morsel, let him remove any dirt on it, then eat it, and not leave it for the Shaitan. And when he has finished let him lick his fingers, for he does not know in which part of his food the blessing is."'