صَحِيحُ مُسْلِمٍ
Sahih Muslim 2033 a
The Book of Drinks
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
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم أَمَرَ بِلَعْقِ الأَصَابِعِ وَالصَّحْفَةِ وَقَالَ إِنَّكُمْ لاَ تَدْرُونَ فِي أَيِّهِ الْبَرَكَةُ .
Jabir reported that Allah's Messenger (ﷺ) commanded the licking of fingers and the dish, saying: You do not know in what portion the blessing lies."
Sahih Muslim, 2033 aSahihصحيح