Musannaf Ibn Abi Shayba 16:225

Abu Bakr narrated to us, he said: Ibn 'Uyaynah narrated to us, from Abu al-Zubayr, from Jabir, that the Prophet (peace and blessings of Allah be upon him) commanded the licking of the fingers and the dish. And he said: "Indeed, you do not know in which part of your food the blessing lies."