Is it valid to respond to someone other than the imam?

The questioner : Is it permissible for him to respond to someone other than the imam, O Khalid? To someone other than his imam?

The Shaykh : No, we have no ruling on that.

The questioner : For example, a person is reading next to you while you are praying, and he makes a mistake.

The Shaykh : No, he has no sin. Why? For two reasons. First, this is listening to someone other than the one to whom listening is prescribed. Second, there is no connection between him and this reader such that he would pay attention to him and respond to him. As for the imam, there is a connection between him and the one behind him. All right, correct? We say: Do not respond to anyone other than your imam. First, because there is no connection between you and him, unlike the imam, for the completion of his prayer is the completion of your prayer. Second, because this occupies the one praying in a manner he was not commanded to do, for he was not commanded to listen to the recitation of anyone other than his imam.