Riyad as-Salihin, Book 3, Hadith 749 (In-Book) ⓘ
Ka'b bin Malik (May Allah be pleased with him) reported: I saw Messenger of Allah eating with three fingers (i.e., the thumb, the index finger and the middle finger) and licking them after having finished the food.[Muslim].
وعن كعب بن مالك رضى الله عنه قال: رأيت رسول الله صلى الله عليه وسلم يأكل بثلاث أصابع ، فإذا فرغ لعقها.