The ruling on praying behind one who holds beliefs regarding the awliya (close friends of Allah) and the like

The questioner:
May Allah reward you and bless you. Honorable Shaykh, this message came from one of the Arab countries. Your brother, who used the letters T, Sh, and Kh as a code for his name, says: Honorable Shaykh, we have a regular imam who leads us in prayer, and we used to pray behind him. But after we learned that he engages in acts of shirk (associating partners with Allah), specifically that he believes the awliya (close friends of Allah) and the righteous people intercede for their followers and that they can cause harm. This person fell ill, and a member of his family also fell ill. My brother and I tried to treat this sick family member with some of the lawful ruqyah (healing by Qur'anic recitation), because we suspected he was afflicted with possession, but he was not convinced by that. Instead, he brought him something from a Hanafi [tomb/shrine] that he and many people believe contains a blessing from a righteous man, because before his death, he left behind a blessing in it containing water. It is well known among those who know Allah that this man used to treat people by unlawful means, that he dealt with the jinn, and that he did not pray at all. When we advised this imam of this mosque and informed him that this matter is shirk and not permissible, he did not respond to this call. Every time we opened this topic with him, he would say, "Leave us alone with this," and he would accuse my brother and me of being innovators. And every time we opened this door, he would immediately stand up. Therefore, we stopped praying behind this man. So please issue a ruling for us, may Allah reward you, regarding praying behind him.

The Shaykh:
There is no doubt that whoever calls upon other than Allah, or believes in a dead person or other than them, such as a tree, a stone, a jinn, or a human, that they can benefit or harm without Allah, that this is major shirk (associating partners with Allah) that takes one out of the religion. What you mentioned about this man regarding this shirk belief in the created beings, it is not permissible for you to pray behind him. Even if you did pray behind him, your prayer would not be valid.
Because his own prayer is not valid; because he is a mushrik (one who associates partners with Allah), and the prayer of whoever prays behind him is not valid. So you did well by distancing yourselves from him after advising him and clarifying the matter to him. When he did not accept the advice and persisted in his error and misguidance, you must distance yourselves from him and not pray behind him. You should warn the other Muslims who pray behind him, warn them of that, and inform them that it is not valid to pray behind one who holds this belief, because this is a trap for the Muslims. The Messenger (peace and blessings be upon him) said: So you must advise your brothers who are ignorant of the reality of this man, or who are ignorant of the legal ruling, and clarify to them that praying behind this man is not permissible, and that this belief is shirk and false. May Allah reward you with good. Yes.

The questioner:
He asks: Is he excused by ignorance after the proof has been established against him?

The Shaykh:
Matters that are apparent, such as tawhid (the oneness of Allah) and shirk (associating partners with Allah), are apparent and clear matters in the Qur'an and the Sunnah. No one is excused by ignorance if the Qur'an has reached him and the Sunnah has reached him. In addition to that, if the words of the scholars have reached him, he is not excused, and he is not ignorant, but he is deliberately opposing the truth. And what indicates that he is not ignorant is that you advised him and he refused to accept the advice. So this is one who is obstinate. Yes.