Will a Muslim not abide eternally in Hell, no matter what their deeds?

The belief of the Ahl al-Sunnah wal-Jama'ah is that whoever dies as a Muslim will not abide eternally in Hellfire, no matter how great their sins may be. They may enter it for a period, or Allah may forgive them, in accordance with the Almighty's saying: "Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills." And the Prophet, peace and blessings be upon him, said: "Whoever testifies that there is no god but Allah alone, without partner... Allah will admit him to Paradise regardless of his deeds." As for the Khawarij and the Mu'tazilah, they hold that the perpetrator of a major sin will abide eternally in Hellfire, contrary to the Ahl al-Sunnah.