Mishkat al-Masabih 21 Foods كتاب الأطعمة 7

وَعَنْ جَابِرٌ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَمَرَ بِلَعْقِ الْأَصَابِعِ وَالصَّفْحَةِ وَقَالَ: ” إِنَّكُمْ لَا تَدْرُونَ: فِي أَيَّهِ الْبَرَكَةُ؟ ” . رَوَاهُ مُسْلِمٌ

Jabir said the Prophet ordered people to lick their fingers and the dish, saying, “You do not know in what portion blessing lies.” Muslim transmitted it.