Is the prayer valid for one who stands with a person in a state of ritual impurity?

The Shaykh : And likewise for one who stands with a person in a state of ritual impurity. Even if the one standing is knowledgeable, the prayer of the second person is valid because he is ignorant and does not know that his companion’s prayer is not valid. However, if he knows that this man is in a state of ritual impurity, then standing with him while knowing that is considered...