The Quran

وَقالَ الَّذينَ كَفَروا لَن نُؤمِنَ بِهٰذَا القُرآنِ وَلا بِالَّذي بَينَ يَدَيهِ ۗ وَلَو تَرىٰ إِذِ الظّالِمونَ مَوقوفونَ عِندَ رَبِّهِم يَرجِعُ بَعضُهُم إِلىٰ بَعضٍ القَولَ يَقولُ الَّذينَ استُضعِفوا لِلَّذينَ استَكبَروا لَولا أَنتُم لَكُنّا مُؤمِنينَ

Muhammad Asad

And [yet,] those who are bent on denying the truth do say, "We shall never believe in this Qur'an, and neither in whatever there still remains of earlier revelations !"¹ But if thou couldst only see [how it will be on Judgment Day,] when these evildoers shall be made to stand before their Sustainer, hurling reproaches back and forth at one another! Those [of them] who had been weak [on earth] will say unto those who had gloried in their arrogance:² "Had it not been for you, we would certainly have been believers!"

For the rendering of ma bayna yadayhi, in relation to the Qur'an, as "whatever there still remains of earlier revelations", see surah 3, note 3. As is evident from the preceding and subsequent verses, the rejection by "those who are bent on denying the truth" of all revelation is motivated by their refusal to believe in resurrection and God's judgment, and, hence, to admit the validity of absolute moral standards as postulated by every higher religion.
I.e., as the "intellectual leaders" of their community.