رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 749
The Book About the Etiquette of Eating
Excellence of Eating with Three Fingers and Licking Them
وَعَنْ جَابِرٍ رضى اللَّه عَنْهُ أَنَّ رَسُولَ اَللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ أَمَرَ بِلَعْقِ الأَصَابِعِ وَالصَّحْفَةِ، وَقَالَ: إِنَّكُمْ لاَ تَدْرُونَ فِي أي طعامكم البركة .((رَوَاهُ مُسْلِم))
Jabir (May Allah be pleased with him) reported: The Messenger of Allah (ﷺ) commanded the licking of fingers and the gleaning of the dish, saying, "You do not know in which portion the blessing lies." [Muslim].
Riyad as-Salihin, 749