Shaykh Wasiuallaah Abbaas said, “If an instructor [of Arabic or Tajweed) has a proper, pure aqeedah and is available to teach a certain branch of knowledge or field of study that he is qualified in, then knowledge must not be taken from other than him.
If such a person is not found, then the knowledge (of Tajweed or Arabic) can be taken from anyone who possesses it (even an innovator), while being aware and guarding oneself against the errors of the one who does not have the correct aqeedah (i.e an innovator).
For if you were to study the Arabic language from someone who explains away the Attributes of Allaah, then he may give you an example of a verse (from the Quran to explain a grammar point), and then explain away one of Allaah’s Attributes.
For this reason, it is necessary to choose the best and most suitable teacher, and if he is not available, then we choose the next best after him, etc.
This is from what the Salaf taught us about this affair (seeking knowledge) being deen (religion), so look to whom you take your deen from!” Ref: bakkah.net
On the other hand Shaykh Uthaymen said, “Nothing is to be taken from a person of innovation (not even Arabic, Tajweed) even if it is knowledge which is not related to their bidah (innovation).
For example, if we found a man who is an innovator but he is good in the Arabic language, Balaagah (Art of composition), Sarf (Morphology) and grammar, do we sit with him and take this knowledge that he possesses or do we abandon him?
We do not sit with him (as sitting with him) would result in two harmful (effects).
The first harmful effect is that he will be fooled by himself and he will believe that he is upon the truth.
The second harmful effect is that the people will be fooled by him due to the students of knowledge coming to and learning from him.
Also the common folk do not differentiate between the knowledge of grammar and the knowledge of aqeedah.
So that is why we hold that it is not allowed to sit with an innovator in totality, even if they could not find Arabic, Grammar and Sarf except with him.” Ref: Salafitalk.net
Posted by Abdul Kareem Ibn Ozzie