Sayyiduna Ka'b bin Malik (may Allah be pleased with him) said: The Noble Prophet (peace and blessings be upon him) used to eat with three fingers and would not clean his hand before licking it. (That is, he would lick them before cleaning them.)
Hadith Referenceسنن دارمي / من كتاب الاطعمة / 2072
Abdullah bin Ka'b or Abdur Rahman bin Ka'b (Hisham bin Urwah was unsure) reported, their father Sayyiduna Ka'b bin Malik (may Allah be pleased with him) narrated that the Noble Prophet (peace and blessings be upon him) used to eat with three fingers, and when he finished eating, he would lick them. Hisham bin Urwah indicated towards the three fingers to explain.
Hadith Referenceسنن دارمي / من كتاب الاطعمة / 2073
Hadith Takhrijاس روایت کی سند جید ہے اور عبدالله و عبدالرحمٰن دونوں سیدنا کعب بن مالک رضی اللہ عنہ کے بیٹے ہیں جو ثقات التابعين میں سے ہیں، اس حدیث کا حوالہ اوپر گذر چکا ہے۔