According to Qur'ān 4:48, to set up partners with Allah is a great offense which Allah will not forgive

According to Qur'ān 4:48, setting up partners with Allah is a great offense which Allah will not forgive, even if He forgives all other sins. This means that associating partners with Allah (known as shirk in Islamic terminology) is considered a grave sin that can lead to eternal punishment in the afterlife. However, there are conditions under which Allah may forgive this sin. The first condition is repentance, which means sincerely regretting the sin and resolving not to commit it again. The second condition is intercession from the Prophet Muhammad (peace be upon him) on behalf of the offender. If these conditions are met, Allah may choose to forgive the sin of shirk. However, it is important to note that shirk is considered one of the most serious sins in Islam, and it is strongly discouraged for Muslims to even approach this sin.