It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) 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 it licked by someone else."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 3499