The ruling on praying behind one who openly commits sin

Question:
Honorable Shaykh, may Allah grant you success. Is it permissible to pray behind one who openly commits sin? And is the prayer valid?

Answer:
And what kind of sin is it? If it entails open sinfulness, then one does not pray behind him. But if it is among the minor sins, none of us is free from them, my brother. There is no one who leads people in prayer who is free from sins. And who is this? We do not know this.
Major sins, yes, the major sins that he openly commits and which are apparent to him. As for the major sins that he conceals, his matter is left to Allah. We do not investigate his actions in his home or in his private places. But if he displays a major sin, or boasts of it and mentions it to people, he is one who openly commits sin, and it is not permissible to pray behind him. Yes.
Except if he is one of those in authority, then one prays behind them for the sake of uniting the word. The Companions used to pray behind al-Hajjaj, and behind Ibn Ziyad, and behind the rulers who were not entirely upright. There were observations against them, yet they prayed behind them.