Riyad as-SalihinChapter 2Hadith 69
Full Sharh — Riyad as-Salihin 69
وعن كعب بن مالك رضى الله عنه قال: رأيت رسول الله صلى الله عليه وسلم يأكل بثلاث أصابع ، فإذا فرغ لعقها.((رواه مسلم))
English Translation
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..
Source
Riyad as-Salihin(رياض الصالحين)
The Book About the Etiquette of Eating
Hadith Number
69