It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) said: "When any one of you eats food, he should not wipe his hand before licking it or having it licked (by someone else)."
Hadith Referenceسنن دارمي / من كتاب الاطعمة / 2065
Hadith Takhrijاس حدیث کی سند صحیح ہے اور حدیث متفق علیہ ہے۔ دیکھئے: [بخاري 5456] ، [مسلم 2031] ، [أبوداؤد 3847] ، [ابن ماجه 3269] ، [أبويعلی 2503] ، [ابن حبان 5252]
Brief Explanation
(Commentary on Hadith 2064)
Here, in this narration and in Sahih Bukhari, the word "mandil" (cloth/napkin) is not mentioned, but in Sahih Muslim it is: «فَلَايَمْسَحْيَدَهُبِالْمَنْدِيْلِ» meaning, "He should not wipe his hands with a napkin before licking them."
In Arabic, "mandil" refers to a cloth handkerchief, which also applies to tissues, papers, etc., used to remove grease and the like after eating.
The Messenger of Allah (sallallahu alayhi wa sallam) instructed to lick the fingers before wiping the hands with a napkin.
There is a narration in Abu Dawud that whoever goes to sleep while there is grease on his hands and does not wash them, and then some harm befalls him, he should blame only himself. [أبوداؤد 3852] In Ibn Majah, there is the addition that he does not know in which morsel of food the blessing lies.
From the above-mentioned hadith, the permissibility of wiping the hands with a napkin is established, and also that hands should definitely be washed after eating, otherwise there is a risk of harm.
(See Hadith No: 2100), and having the wife or servant lick the fingers is also a means of avoiding waste of sustenance.
Those worldly people who consider licking fingers to be against etiquette are deprived of following the Sunnah and its reality. May Allah guide them.