رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 748
The Book About the Etiquette of Eating
Excellence of Eating with Three Fingers and Licking Them
وَعَنْ كَعْبِ بْنِ مَالِكٍ رضى اللَّه عَنْهُ قَالَ: رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ يَأْكُلُ بِثَلاَثِ أَصَابِعَ ، فَإِذَا فَرَغَ لَعِقَهَا.((رَوَاهُ مُسْلِم))
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].
Riyad as-Salihin, 748