The Prophet ﷺ said, "When one of you eats, he should not wipe his hand until he licks it or has it licked."
قال أبي و قال سفيان عن عمرو عن عطاء
أن النبي ﷺ قال إذا أكل أحدكم فلا يمسح يده حتى يلعقها أو يلعقها
Its isnad is sahih. Bukhari and Muslim and others also narrated it, as in al-Muntaqa 4688, 4689. This is one of those hadiths that the pampered, "civilized" ones among us, the slaves of Europe in our lands, talk about and find objectionable! The more refined among them even claims it is a fabricated hadith, simply because he does not like it and it does not suit his taste! They find it disgusting to eat with the hands, which are the instrument for food that Allah created, and which the eater can trust to be clean and pure, so long as they are as clean and pure as the cleanliness of the believers. As for manufactured eating utensils, it is far less certain that the eater can be confident of their cleanliness, unless he washes them himself with his own hand. So which of the two is actually cleaner?And what harm is there if someone else licks his fingers, when that person is a member of his household or someone close to him and in regular contact with him, so long as each of them trusts in the cleanliness and purity of the other, and trusts that he has no disease to be feared or found repulsive?See also 2672.