that the Messenger of Allah ﷺ said: "Whoever is asked about some knowledge that he knows, then he conceals it, he will be bridled with bridle of fire."  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ سُئِلَ عَنْ عِلْمٍ عَلِمَهُ ثُمَّ كَتَمَهُ أُلْجِمَ يَوْمَ الْقِيَامَةِ بِلِجَامٍ مِنْ نَارٍ وَفِي الْبَابِ عَنْ جَابِرٍ وَعَبْدِ اللَّهِ بْنِ عَمْرٍو