ٱلَّذِينَ ءَاتَيْنَـٰهُمُ ٱلْكِتَـٰبَ يَعْرِفُونَهُۥ كَمَا يَعْرِفُونَ أَبْنَآءَهُمُ ۘ ٱلَّذِينَ خَسِرُوٓا۟ أَنفُسَهُمْ فَهُمْ لَا يُؤْمِنُونَ Qur’an Al-An'am (6:20)Allatheena ataynahumu alkitaba yaAArifoonahu kama yaAArifoona abnaahum allatheena khasiroo anfusahum fahum la yuminoona
I.e., the truth of God's transcendental uniqueness and oneness, which is stressed in all authentic scriptures.
Cf. ii. 146 and n. 151. In both passages the pronoun translated "this" may mean "him" and refer to Muhammad the Apostle of God, as some commentators think.