It is reported that Imām Al-Awzā’ī – Allāh have mercy on him – used to say:

Whoever hides his heresy (bid’ah) from us, his companionship is not hidden from us.

Ibn Battah, Al-Ibānah Al-Kubrā article 420.

It is reported that when Sufyān Al-Thawrī – Allāh have mercy on him – came to Baṣrah he started to look into the matter of Al-Rabī’ – i.e. Ibn Ṣabīḥ
⁽¹⁾ – and his status amongst the people. [Sufyān] asked, “What does he believe?” [People] replied, “He believes in nothing but the Sunnah.” He asked, “Who are his companions?” They replied, “The People of Qadr (those who denied Allāh’s pre-decree).” He said, “Then he is a Qadarī (like them).”

Ibid. article 421.

⁽¹⁾ Al-Rabī’ b. Ṣabīḥ is described in biographies as being a truthful reporter, but with a bad memory; a devout worshipper and a mujāhid.

It is reported that Al-Fuḍayl b. ‘Ayyāḍ – Allāh have mercy on him – said:

The souls [of people] are in groups gathered together: those of them that identify with each other come together, and those that are different diverge. It is not possible for an adherent of the Sunnah to incline towards an adherent of Bid’ah except out of hypocrisy (nifāq).

Ibid. article 429.