Sahih Muslim Book - 54, Hadith - 7544

حَدَّثَنِى هَارُونُ بْنُ عَبْدِ اللَّهِ حَدَّثَنَا أَبُو النَّضْرِ هَاشِمُ بْنُ الْقَاسِمِ اللَّيْثِىُّ حَدَّثَنَا أَبُو مُعَاوِيَةَ - يَعْنِى شَيْبَانَ - عَنْ مَنْصُورِ بْنِ الْمُعْتَمِرِ عَنْ سَعِيدِ بْنِ جُبَيْرٍ عَنِ ابْنِ عَبَّاسٍ قَالَ نَزَلَتْ هَذِهِ الآيَةُ بِمَكَّةَ (وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ) إِلَى قَوْلِهِ (مُهَانًا) فَقَالَ الْمُشْرِكُونَ وَمَا يُغْنِى عَنَّا الإِسْلاَمُ وَقَدْ عَدَلْنَا بِاللَّهِ وَقَدْ قَتَلْنَا النَّفْسَ الَّتِى حَرَّمَ اللَّهُ وَأَتَيْنَا الْفَوَاحِشَ فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ (إِلاَّ مَنْ تَابَ وَآمَنَ وَعَمِلَ عَمَلاً صَالِحًا) إِلَى آخِرِ الآيَةِ. قَالَ فَأَمَّا مَنْ دَخَلَ فِى الإِسْلاَمِ وَعَقَلَهُ ثُمَّ قَتَلَ فَلاَ تَوْبَةَ لَهُ.

It was narrated from Sa'eed bin Jubair that Ibn 'Abbas said: "This Verse was revealed in Makkah: "And those who invoke not any other ilah (god) along with Allah, nor kill such person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse - and whoever does this, shall receive the punishment. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace." The idolaters said: 'Islam is of no avail for us, because we have ascribed peers to Allah, and we have killed those whom Allah has forbidden killing, and we have committed immoral deeds. Then Allah revealed: "Except those who repent and believe, and do righteous deeds; for those, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful.'' He (Ibn 'Abbas) said: "As for the one who enters Islam and understands it, then kills someone, there is no repentance for him."