Sayyiduna Amir bin Rabi'ah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) used to eat with three fingers, and when he had finished (eating), he would lick those fingers.
Al-Bazzar recorded it, and al-Tabarani recorded it in abridged form, only the part about licking the fingers. Its chain contains Asim bin Ubaydullah, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأطعمة / 7923