The Bee - 16:35
Those who associate partners, if Allah had not willed, neither we nor our ancestors would have served anything besides Him, nor would we have forbidden anything besides what He has forbidden. So did those before them. Does the messenger have any duty other than to make clear?
Related:
The Cattle/6:148
"Those who associate partners will say: "If Allah had not willed, neither we nor our fathers would have associated partners, nor would we have forbidden anything."And those before them denied in the same way until they tasted Our torment. Say: "Do you have any knowledge with you that you can show us? You follow only conjecture (doubtful and contradictory narrations) and you are only guessing."