Al-Anbya 21:5

Bal qaloo adghathu ahlaminbali iftarahu bal huwa shaAAirun falya/tinabi-ayatin kama orsila al-awwaloon

But they say, "[The revelation is but] a mixture of false dreams; rather, he has invented it; rather, he is a poet. So let him bring us a sign just as the previous [messengers] were sent [with miracles]."

Further they said, “(The Qur’ān is) a mixture of jumble dreams. Rather, he (the prophet) has fabricated it. Rather, he is a poet. So, let him bring a sign to us, as the earlier ones were sent with.”