Al-Furqan 25:4

Waqala allatheena kafaroo in hathailla ifkun iftarahu waaAAanahu AAalayhiqawmun akharoona faqad jaoo thulmanwazoora

And those who disbelieve say, "This [Qur’ān] is not except a falsehood he invented, and another people assisted him in it." But they have committed an injustice and a lie.

The disbelievers said, “This is nothing but a lie he (the messenger) has fabricated and some other people have helped him in it.” Thus they came up with sheer injustice and falsehood.