Jabir (May Allah be pleased with him) reported:
Messenger of Allah (ﷺ) commanded the licking of fingers and the gleaning of the dish, saying, "You do not know in which portion the blessing lies."[Muslim]. (JA)
App reference (JA): Book 3, Hadith 23 (JA)
Arabic/English book reference (JA): Book 3, Hadith 750 (JA)