6:23
There will then be (left) no subterfuge for them but to say: “By Allah our Lord, we were not those who joined gods with Allah.”
The following excerpt is taken from “The Study Quran” under the commentary of the above verse:
Al-Rāzī suggests that major sins may represent different forms of kufr (disbelief), including disbelief in God, the prophets, the Last Day, or the Sacred Law. This interpretation aligns with Qur’ān 4:48, which states that God forgives all sins except shirk (idolatry) (Nasr et al., 2015). Furthermore, Sufi commentators generally maintain that the gravest sin is shirk, yet they broaden its meaning to include excessive attachment to worldly matters or the assertion of the independent existence of the self in a manner that undermines complete devotion and reliance upon God. In this context, a well-known Sufi saying—sometimes attributed to Rābiʿah al-ʿAdawiyyah (d. 801)—states: “Your existence is a sin to which no other sin can be compared!” (Nasr et al., 2015).
References:
Nasr, Hossein (2015). Study Quran.