Regarding Scholars Who Err In Their Ijtihaad, By Ibn Taymiyyah
There is no doubt that one speaks ill against these types of scholars except for those whom Allaah has led astray and blinded. So if one of these scholars errs in an issue from the issues in which Ijtihaad is allowed, it must be clarified, but not in the manner of condemning.
Ibn Taymiyyah said in this regard:
“So whoever is known to have (the ability to perform) the allowable ijtihaad, then it is not permissible for him to be mentioned in a manner of condemnation or blame, because Allaah has forgiven his error.
Instead, it is an obligation due to what he possesses of Eemaan and taqwaa to show loyalty and love to him, and to fulfill what Allaah has mandated from his rights, such as praising him, making du’aa for him, and so on.”
[Majmoo’ Al-Fataawaa, 28/234]