Nasai

A believer intentionally committing murder is an extremely grave sin. In the Noble Qur’an, its punishment is described as eternal Hellfire, Allah’s wrath, curse, and a tremendous torment. No other sin has been assigned such a punishment. Therefore, it is narrated from Ibn Abbas (radi Allahu anhu) that the repentance of such a person is not accepted; he will have to endure the aforementioned punishments. Or, if in this world he gives retribution (qisas), meaning he is killed in retaliation, then the prescribed punishment erases the sin; otherwise, it will not be forgiven. In any case, this is the most important of the rights of people (huquq al-‘ibad), and Allah Ta‘ala Himself will not forgive the violation of people’s rights. In this hadith as well, it is mentioned alongside disbelief (kufr). Thus, intentionally and unjustly killing a believer is tantamount to disbelief. May Allah protect us. Other sins may be erased in exchange for good deeds, but this is such a sin that it cannot be erased even in exchange for good deeds—except for whom Allah has mercy. Disbelief (kufr), polytheism (shirk), and hypocrisy (nifaq) are also of this nature. However, if a person, while in a state of disbelief, kills another person, then upon accepting Islam, that sin is forgiven. (Further details are coming ahead.)