When one of you eats, he must not wipe his hand with a handkerchief till he licks it or gives it to someone to lick. (Using translation from Abū Dāʾūd 3847)  

عَنِ النَّبِيِّ ﷺ قَالَ «إِذَا أَكَلَ أَحَدُكُمْ فَلَا يَمْسَحْ يَدَهُ بِالْمِنْدِيلِ حَتَّى يَلْعَقَهَا أَوْ يُلْعِقَهَا»