كتاب الأشربة
36  
The Book of Drinks
(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
(18)
باب اسْتِحْبَابِ لَعْقِ الأَصَابِعِ وَالْقَصْعَةِ وَأَكْلِ اللُّقْمَةِ السَّاقِطَةِ بَعْدَ مَسْحِ مَا يُصِيبُهَا مِنْ أَذًى وَكَرَاهَةِ مَسْحِ الْيَدِ قَبْلَ لَعْقِهَا
Sahih Muslim 2033 f

Jabir reported from Allah's Messenger. (ﷺ) about mentioning the licking (of fingers) and the (falling of) the mouthful.

وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا مُحَمَّدُ بْنُ فُضَيْلٍ، عَنِ الأَعْمَشِ، عَنْ أَبِي، صَالِحٍ وَأَبِي سُفْيَانَ عَنْ جَابِرٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم فِي ذِكْرِ اللَّعْقِ ‏.‏ وَعَنْ أَبِي سُفْيَانَ عَنْ جَابِرٍ عَنِ النَّبِيِّ صلى الله عليه وسلم وَذَكَرَ اللُّقْمَةَ نَحْوَ حَدِيثِهِمَا ‏.‏
Reference : Sahih Muslim 2033f
In-book reference : Book 36, Hadith 179
USC-MSA web (English) reference : Book 23, Hadith 5048
  (deprecated numbering scheme)