It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When any one of you eats food, he should not wipe his hands with a towel until he has licked his fingers himself or given them to someone else to lick, because he does not know in which part of his food the blessing lies."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14221