It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them) that the Messenger of Allah (peace and blessings be upon him) said: "When any one of you eats food, he should not wipe his hand before licking it or having someone else lick it." Abu Az-Zubair says that I heard this same hadith from Sayyiduna Jabir (may Allah be pleased with him) in this way: "The bowl should not be lifted until either he himself or someone else has licked it, because there is blessing in the last part of the food."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2672