Is the prayer valid behind an Imam who prayed over a deceased person who used to utter words of disbelief (kufr), polytheism (shirk), and insults, and did not pray?

It has been previously explained that there is a difference of opinion regarding praying over one who abandoned prayer. As for one who uttered words of disbelief, and the conditions for declaring him a disbeliever were met, and there were no impediments, and he did not return to Islam before his death, one should not pray over him. Prayer behind an Imam who prayed over a disbeliever is valid, but his action is a sin that necessitates repentance. Praying behind someone else is more preferable in this situation. One should have a good opinion of the Imam, as he might not believe the deceased was a disbeliever or might know that he repented.