Is it permissible to pray in a mosque built with money that might be mixed with funds earned from selling prohibited things, and will those who donated and contributed to its construction be rewarded?

If a mosque is built with illicit money, the builder receives no reward, for Allah is good and accepts only what is good. As for whoever contributed with their lawful money, their reward is certain if their intention was sincere. Prayer in such a mosque is permissible, because the owner of illicit money disposes of it for public welfare, such as building mosques.