What is the ruling on the prayer of one who felt wetness and doubted whether it was madhiy (pre-seminal fluid) or maniy (seminal fluid), and then prayed in congregation, only to discover madhiy on his underwear, knowing that he frequently experiences madhiy? And what is the ruling on praying in a mosque where some people perform ablution with bare feet after relieving themselves and then enter the mosque with them?

The questioner must beware of Satan's whisperings concerning purity. As long as he found traces of madhy on his garment shortly after his hesitation about the wetness, this indicates that the wetness was madhy and he prayed while afflicted by it. Therefore, he must wash the madhy from his body and garment, wash his private parts, perform ablution (wudu'), and repeat the prayer because he prayed without ablution. As for the feet of those who perform ablution and go to the mosque barefoot, they are pure, and the places they step on in the mosque remain pure. The default state of things is purity until certainty of impurity is established, and a sudden doubt does not harm.