Do we declare the Khawarij and the Mu'tazilah to be disbelievers?

Scholars have differed regarding whether the Khawarij and Mu'tazilah are disbelievers. Some have held that they are not disbelievers, citing the hadith about the division of the Ummah, which counted them as part of it. Also, Al-Khattabi said: "The Prophet, peace and blessings be upon him, made all of them part of his Ummah." Al-Adawi narrated concerning the Mu'tazilah that the preponderant opinion is that they are disobedient, not disbelievers. Al-Nawawi narrated from Al-Isfarayini that the Khawarij are not disbelievers. Ibn 'Abidin narrated from Al-Nahr that the truth is not to declare disbelievers those who face the Qiblah. This opinion is the most preponderant, because those who declared them disbelievers based their view on the premise that the logical consequence of a doctrine is a doctrine itself, which is incorrect. Furthermore, they only said what they did due to a perceived valid religious proof, even if they erred in its interpretation.