What is the proof from the Holy Quran that all monotheistic Muslims will enter Paradise no matter what sins they commit?

Whoever dies from among the Muslims who committed acts of disobedience will not abide eternally in the Fire. Rather, their fate is subject to Allah’s will: if He wills, He will punish them and then admit them into Paradise, and if He wills, He will forgive them. The Ahlus-Sunnah (Sunnis) have cited as evidence for this 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 persistence of the brotherhood of faith despite major sins like murder, as in His saying: "So whoever is pardoned a thing by his brother," and His saying: "The believers are nothing but brothers, so make reconciliation between your two brothers." From the Sunnah, there is the hadith of 'Ubadah ibn As-Samit regarding the pledge of allegiance: "And whoever commits any of that [sins] and Allah conceals it, then his affair is with Allah; if He wills, He will forgive him, and if He wills, He will punish him," and the hadith of Abu Sa'id Al-Khudri regarding the expulsion from the Fire of anyone who had an atom's weight of faith in their heart.