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
وَحَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا هِشَامٌ، عَنْ عَبْدِ الرَّحْمَنِ، بْنِ سَعْدٍ أَنَّ عَبْدَ الرَّحْمَنِ بْنَ كَعْبِ بْنِ مَالِكٍ، - أَوْ عَبْدَ اللَّهِ بْنَ كَعْبٍ - أَخْبَرَهُ عَنْ أَبِيهِ، كَعْبٍ أَنَّهُ حَدَّثَهُمْ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَأْكُلُ بِثَلاَثِ أَصَابِعَ فَإِذَا فَرَغَ لَعِقَهَا .
'Abdullah b. Ka'b reported that his father Ka'b narrated to him that Allah's Messenger (ﷺ) used to eat with three fingers and when he had finished (eating), he licked them.
Reference : Sahih Muslim 2032cIn-book reference : Book 36, Hadith 172USC-MSA web (English) reference : Book 23, Hadith 5041