Word by Word Analysis

وَلَمَّا جَآءَهُمْ رَسُولٌ مِّنْ عِندِ ٱللَّهِ مُصَدِّقٌ لِّمَا مَعَهُمْ نَبَذَ فَرِيقٌ مِّنَ ٱلَّذِينَ أُوتُوا۟ ٱلْكِتَـٰبَ كِتَـٰبَ ٱللَّهِ وَرَآءَ ظُهُورِهِمْ كَأَنَّهُمْ لَا يَعْلَمُونَ 101

And when a messenger from Allāh came to them confirming that which was with them, a party of those who had been given the Scripture threw the Scripture of Allāh [i.e., the Torah] behind their backs as if they did not know [what it contained].