Inform the shelterers of the innovators about this praiseworthy characteristic of the Imaams of the Sunnah
بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ
Shaikh Saaleh Aala Shaikh (may Allaah preserve him) said:
Giving importance to the Sunnah and refuting the innovators is [something] manifest from the Imaams of Islaam. Indeed, they [devoted] their lives in refuting the innovators, but not the ‘Kuffaar Asliyyeen’ [i.e. those who do not ascribe themselves to Islaam].
And if you look at the statements of Imaam Ahmad, Sufyaan, Hammaad Bin Zayd, Hammaad Bin Salamah, Nu-aym Ibn Hammaad, Al-Awzaa’ee, Ishaaq, Ali Ibn Al-Madeenee and their likes amongst the Imaams of the Sunnah, you will find that their speech and striving was [devoted] in refuting the innovators and declaring their principles faulty, even though they [i.e. the innovators] were still within the fold of Islaam.
They [i.e. the Imaams of the Sunnah] did not busy themselves with refuting the Jews, the Christians and others [instead they refuted the innovators within Islam], because the evil of the innovators is not manifested to the people of Islaam and the people of Islaam are not safe from it. As for the Kaafir Asliy [i.e. the one who does not ascribe himself to Islaam], the harm in [his religion] is manifest and clear to every Muslim.
[Paraphrased & abridged. For further details, see Sharh Lum-atil Ittiqaad: page 155]