And most of them follow nothing but conjecture:

Surah Yunus, Verse 35:
قُلْ هَلْ مِن شُرَكَائِكُم مَّن يَهْدِي إِلَى الْحَقِّ قُلِ اللَّهُ يَهْدِي لِلْحَقِّ أَفَمَن يَهْدِي إِلَى الْحَقِّ أَحَقُّ أَن يُتَّبَعَ أَمَّن لَّا يَهِدِّي إِلَّا أَن يُهْدَىٰ فَمَا لَكُمْ كَيْفَ تَحْكُمُونَ
Say: “Is there of your (Allah’s so-called) partners one that guides to the truth?” Say: “It is Allah Who guides to the truth. Is then He, Who gives guidance to the truth, more worthy to be followed, or he who finds not guidance (himself) unless he is guided? Then, what is the matter with you? How judge you?”
Surah Yunus, Verse 36:
وَمَا يَتَّبِعُ أَكْثَرُهُمْ إِلَّا ظَنًّا إِنَّ الظَّنَّ لَا يُغْنِي مِنَ الْحَقِّ شَيْئًا إِنَّ اللَّهَ عَلِيمٌ بِمَا يَفْعَلُونَ
And most of them follow nothing but conjecture. Certainly, conjecture can be of no avail against the truth. Surely, Allah is All-Aware of what they do.
Surah Yunus, Verse 37:
وَمَا كَانَ هَٰذَا الْقُرْآنُ أَن يُفْتَرَىٰ مِن دُونِ اللَّهِ وَلَٰكِن تَصْدِيقَ الَّذِي بَيْنَ يَدَيْهِ وَتَفْصِيلَ الْكِتَابِ لَا رَيْبَ فِيهِ مِن رَّبِّ الْعَالَمِينَ
And this Quran is not such as could ever be produced by other than Allah (Lord of the heavens and the earth), but it is a confirmation of (the revelation) which was before it [i.e. the Taurat (Torah), and the Injeel (Gospel), etc.], and a full explanation of the Book (i.e. laws and orders, etc, decreed for mankind) – wherein there is no doubt from the the Lord of the ‘Alamin (mankind, jinns, and all that exists).
(English – Mohsin Khan)