The Book of Drinks
36/18. Chapter:
It is recommended to lick one's fingers and wipe the bowl, and to eat a piece of food that is dropped after removing any dirt on it. It is disliked to wipe one's hand before licking it, because of the possibility that the blessing of the food may be in that remaining part. The Sunnah is to eat with three fingers
Sahih Muslim
وَحَدَّثَنِيهِ أَبُو بَكْرِ بْنُ نَافِعٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - يَعْنِي ابْنَ مَهْدِيٍّ - قَالاَ حَدَّثَنَا حَمَّادٌ، بِهَذَا الإِسْنَادِ غَيْرَ أَنَّهُ قَالَ " وَلْيَسْلُتْ أَحْدُكُمُ الصَّحْفَةَ " . وَقَالَ " فِي أَىِّ طَعَامِكُمُ الْبَرَكَةُ أَوْ يُبَارَكُ لَكُمْ " .
This hadith has been reported on the authority of Hammad with the same chain of transmitters, but with a slight variation of wording.
Reference : Sahih Muslim 2035bIn-book reference : Book 36, Hadith 182USC-MSA web (English) reference : Book 23, Hadith 5050