The Messenger of Allah ﷺ used to eat with three fingers, and when he finished, he would lick them.
أن رسول الله ﷺ كان يأكل بثلاث أصابع، فإذا فرغ لعقها.
Muslim reported it in the Book of Drinks (132:2032) from Muhammad bin Abdullah bin Numayr, who said, my father narrated to us, Hisham narrated to us from Abdul-Rahman bin Saad, that Abdul-Rahman bin Kaab bin Malik or Abdullah bin Kaab informed him, from his father Kaab, that he narrated it to them, and he mentioned it. In one version, "and he would lick his hand before wiping it."Tirmidhi reported it in Shamail (132) from Muhammad bin Bashshar, who said, Abdul-Rahman bin Mahdi narrated to us, from Sufyan, from Saad bin Ibrahim, from Ibn Kaab bin Malik, from his father, that the Prophet ﷺ used to lick his fingers three times. This is shadhdh (anomalous).Tirmidhi said, someone other than Muhammad bin Bashshar reported this hadith and said, "he would lick his three fingers."I say, it is as he said. Muslim reported it (131:2032) from three trustworthy narrators, namely Abu Bakr bin Abu Shayba, Zuhayr bin Harb, and Muhammad bin Hatim, who said, Ibn Mahdi narrated to us, from Sufyan, from Saad bin Ibrahim, from Ibn Kaab bin Malik, from his father, who said, I saw the Prophet ﷺ lick his three fingers.