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Jabir said the Prophet (ﷺ) ordered people to lick their fingers and the dish, saying, “You do not know in what portion blessing lies.” Muslim transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ جَابِرٌ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَمَرَ بِلَعْقِ الْأَصَابِعِ وَالصَّفْحَةِ وَقَالَ: " إِنَّكُمْ لَا تَدْرُونَ: فِي أَيَّهِ الْبَرَكَةُ؟ ". رَوَاهُ مُسْلِمٌ
sunnah.com