The Ruling on the Leading of Prayer by a Sinner

Q: What is the ruling on the leading of prayer by one who commits some of the sins, such as smoking, shaving the beard, letting the garment hang below the ankles, or the like of that?

A: His prayer is valid if he performs it as Allah has prescribed, by the consensus of the scholars, and likewise the prayer of the one behind him, if he is the imam, according to the most correct of the two opinions of the scholars.
As for the disbeliever, his prayer is not valid, nor is the prayer of the one behind him, due to the absence of its condition, which is Islam. However, it is obligatory for the responsible authorities to choose for the leading of prayer one who is known for knowledge, virtue, and justice, as much as possible. And success is from Allah.