Arabic text
عن كعب بن مالك رضي الله عنه قال: رأيتُ رسولَ اللهِ صلى الله عليه وسلم يأكلُ بثلاثِ أَصَابِعَ، فإذا فَرَغَ لَعِقَهَا.
Translation
Ka‘b ibn Mālik (may Allah be pleased with him) reported: I saw the Messenger of Allah (may Allah's peace and blessings be upon him) eating with three fingers, and when he finished eating, he would lick them.
Explanation
The Prophet (may Allah's peace and blessings be upon him) used to eat with three fingers, and he wouldn't use his other fingers, except when necessary. And, when he had finished eating, he would lick his fingers.
Source: HadeethEnc.com