كتاب الأشربة
36  
The Book of Drinks
(18)
Chapter: It is recommended to lick one's fingers and wipe the bowl, and to eat a piece of food that is dropped after removing any dirt on it. It is disliked to wipe one's hand before licking it, because of the possibility that the blessing of the food may be in that remaining part. The Sunnah is to eat with three fingers
(18)
باب اسْتِحْبَابِ لَعْقِ الأَصَابِعِ وَالْقَصْعَةِ وَأَكْلِ اللُّقْمَةِ السَّاقِطَةِ بَعْدَ مَسْحِ مَا يُصِيبُهَا مِنْ أَذًى وَكَرَاهَةِ مَسْحِ الْيَدِ قَبْلَ لَعْقِهَا
Sahih Muslim 2035 b

This hadith has been reported on the authority of Hammad with the same chain of transmitters, but with a slight variation of wording.

وَحَدَّثَنِيهِ أَبُو بَكْرِ بْنُ نَافِعٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - يَعْنِي ابْنَ مَهْدِيٍّ - قَالاَ حَدَّثَنَا حَمَّادٌ، بِهَذَا الإِسْنَادِ غَيْرَ أَنَّهُ قَالَ ‏"‏ وَلْيَسْلُتْ أَحْدُكُمُ الصَّحْفَةَ ‏"‏ ‏.‏ وَقَالَ ‏"‏ فِي أَىِّ طَعَامِكُمُ الْبَرَكَةُ أَوْ يُبَارَكُ لَكُمْ ‏"‏ ‏.‏
Reference : Sahih Muslim 2035b
In-book reference : Book 36, Hadith 182
USC-MSA web (English) reference : Book 23, Hadith 5050
  (deprecated numbering scheme)