willful concealment of truth

ٱلَّذِينَ ءَاتَيْنَـٰهُمُ ٱلْكِتَـٰبَ يَعْرِفُونَهُۥ كَمَا يَعْرِفُونَ أَبْنَآءَهُمْ ۖ وَإِنَّ فَرِيقًا مِّنْهُمْ لَيَكْتُمُونَ ٱلْحَقَّ وَهُمْ يَعْلَمُونَ

Those to whom We gave the Scripture know him [i.e., Prophet Muḥammad (ﷺ)] as they know their own sons. But indeed, a party of them conceal the truth while they know [it].