Sheikh Ali Naasir Al-Faqeehee (hafidha-hullaah) said:

As for the mistaken one in some of the matters (of the religion), the one who is known for his minhaj (correct methodology), his praiseworthy manner and Islamic legislated knowledge, then his mistake does not remove his status nor reduce his rank. If he is alive, then it is a must to clarify to him the mistake in a wise manner that which is known between the scholars based upon cooperating in accordance with righteousness and piety because religion is advice.

You put the advice to the student of knowledge based upon his status with good manners and respect showing the truth with its proof not in an aggressive manner and not arrogantly towering over the person haughtily. Rather, with wisdom and beautiful preaching. This is what is sought from the advice. The unity is kept and love and brotherhood for the sake of Allāh remains for indeed the believers are brothers.

If the mistaken one has returned to his Lord (passed away) then he is to be supplicated for as perfection is for the prophets alone. The mistakes of other than the prophets are clarified to the people so that the people don’t follow their mistakes in those matters. [Al-Bidcah Dhawabidtuha wa Atharuha as-Sayi’a fil Ummah p.24]

Translated by Ustaadh Abdulilah Lahmaaami