Ibn ʿAbbās (may Allah be pleased with them both) reported that the Messenger of Allah ﷺ said: "When one of you eats food, let him not wipe his fingers until he licks them or has them licked." Agreed upon.
١٠٩ - باب استحباب الأكل بثلاث أصابع، واستحباب لعق الأصابع، وكراهة مسحها قبل لعقها واستحباب لعق القصعة وأخذ اللقمة التي تسقط منه وأكلها، ومسحها بعد اللعق بالساعد والقدم وغيرها
Ibn ʿAbbās (may Allah be pleased with them both) reported that the Messenger of Allah ﷺ said: "When one of you eats food, let him not wipe his fingers until he licks them or has them licked." Agreed upon.
Kaʿb ibn Mālik (may Allah be pleased with him) said: I saw the Messenger of Allah ﷺ eating with three fingers, and when he finished he licked them. Narrated by Muslim.
Jābir (may Allah be pleased with him) reported that the Messenger of Allah ﷺ commanded the licking of the fingers and the dish, and said: "You do not know in which part of your food the blessing lies." Narrated by Muslim.
From him (Jābir) also: the Messenger of Allah ﷺ said: "When the morsel of one of you falls, let him pick it up and remove whatever harm is on it, and let him eat it; let him not leave it for Satan. And let him not wipe his hand with the napkin until he has licked his fingers, for he does not know in which part of his food the blessing lies." Narrated by Muslim.
From him (Jābir) also: the Messenger of Allah ﷺ said: "Satan is present with one of you at everything he does, even to the point of being present with him at his meal. So when the morsel of one of you falls, let him pick it up and remove whatever harm is on it, then let him eat it and not leave it for Satan. And when he finishes, let him lick his fingers, for he does not know in which part of his food the blessing lies." Narrated by Muslim.
Anas (may Allah be pleased with him) said: When the Messenger of Allah ﷺ ate food, he would lick his three fingers, and he said: "When the morsel of one of you falls, let him pick it up and remove the harm from it, and let him eat it; let him not leave it for Satan." And he commanded us to wipe the bowl clean, and said: "You do not know in which part of your food the blessing lies." Narrated by Muslim.
Saʿīd ibn al-Ḥārith reported that he asked Jābir (may Allah be pleased with him) about ablution from what fire has touched. He said: "No. In the time of the Prophet ﷺ we would find such food only rarely, and when we did find it, we had no napkins except our palms, our forearms, and our feet. Then we would pray and not perform ablution." Narrated by al-Bukhārī.