Is it permissible to wash undergarments that have become impure along with other clothes in the same basin, and what is the ruling on praying in clothes that became impure unknowingly?

The ruling on washing impure clothes with pure ones, and the ruling on praying with impure clothes unknowingly, has been previously explained. The preponderant opinion is that his prayer is valid, based on the statement of Sheikh al-Islam Ibn Taymiyyah: "If he prayed and there was impurity on his body or clothes, and he did not know about it until after the prayer, he is not obliged to repeat it." As for the method of washing, it is safer to pour water on the impurity first.