Riyad as-Saliheen 749
Ka'b bin Malik (May Allah be pleased with him) reported:
I saw Messenger of Allah ﷺ 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 ﷺ يأكل بثلاث أصابع ، فإذا فرغ لعقها.
Classification
Sahih (Authentic)
References
Riyad as-Saliheen 749
Riyad as-Saliheen Book of Etiquette of Eating, Hadith 22