1. lmaam Ahmad reports in his Musnad (4/278) with hasan isnaad narration of Nu'maan ibn Basheer: Abu Umaamah al-Baahilee, radiallaahu 'anhu, said, "Stick to the main body (as-Sawaadul - a'dham), so a man said, "What is the 'Main Body'? So Abu Umaamah said,'This Ayah(54) in Soorah an-Noor:
"But if you turn away,he Muhammad is oniy responsible for the duty placed on him and you for that placed on you."
Ibn Mas'ood, radiallahu 'anhu, said,"The Jamaa'ah is what conforms to the truth, even if you are alone." Reported by Ibn'Asaakir in Taareekh Dimashq with a saheeh isnaad as pointed out by Shaikh al-Albaanee in al-Mishkaat (1/61).
2. Allaah, the Most High, did not only warn against opposing His Messenger sallallahu alaihiwasallam, but also warned against the following of any way other than that of the first Believers: the Companions, radiallaahu 'anhum, amongst whom the Qur'aan was sent down and who learned directly from the Messenger sallallahu alaihiwasallam. Allaah, the Most High says:
If anyone contends with the Messenger even after guidance has been plainly conveyed to him and follows a path other than that of the Believers (i.e. the Companions), We shall leave him in the path he has chosen and land him in Hell. What an evil refuge! (Surah an-Nisaa' (4):115)
So he who totally abondons their way and instead follows the way of the devils, like the extreme Raafidess, Baatinees and the extreme Soofees who worship others besides Allaah, then he has left the religion.