WHICH PART OF THE FOOD IS BLESSED? H 760 "After the Prophet, praise and peace be upon him, had finished eating he would lick his three fingers and say, 'If a mouthful of food should fall from your hand, you should pick it up, remove any dirt from it and eat it. Do not leave it for satan.' He also told us to wipe our plate saying, 'You do not know which part of your food is blessed.'" R 760 Muslim with a chain up to Anas who related that the Prophet, praise and peace be upon him, said this.
752- وعن أنسٍ رضي الله عنه ، قَالَ : كَانَ رسولُ الله صلى الله عليه وآله وسلم إِذَا أكَلَ طَعَاماً ، لَعِقَ أصَابِعَهُ الثَّلاَثَ ، وقال : "إِذَا سقَطَتْ لُقْمَةُ أحَدِكُمْ فَلْيَأخُذْهَا ، ولْيُمِطْ عنها الأذى ، وَليَأكُلْهَا ، وَلاَ يَدَعْها لِلْشَّيْطَان" وأمَرَنا أن نَسْلُتَ القَصْعَةَ ، وقال : "إنَّكُمْ لا تَدْرُونَ في أيِّ طَعَامِكُمُ البَرَكَةُ" رواه مسلم .