It is reported that Al-Fuḍayl b. ʿAyyāḍ – Allāh have mercy on him – said, “Whoever helps an adherent of bid’ah (heretic) has helped in the destruction of Islam.”
Abū Nu’aym, Ḥilyatu Al-Awliyā` Vol. 1 p398.
It is reported that Abū Isḥāq Al-Hamdānī and Ibrāhīm b. Maysarah said, “Whoever respects an adherent of bid’ah has helped in the destruction of Islam.”
Reported from Al-Hamdānī by Al-Ājurrī, Al-Sharī’ah Vol. 5 p260; and from Ibn Maysarah by Al-Lālakā`ī, Sharḥ Usūl I’tiqād Ahl Al-Sunnah Vol. 1 p265.