The verse "If a man kills a believer intentionally, his recompense is Hell to abide therein for ever" was revealed six months after the verse "And those who invoke not with Allah any other god, nor slay such life as Allah has made sacred, except for just cause in Surat al-Furqan.
سَمِعْتُ زَيْدَ بْنَ ثَابِتٍ فِي هَذَا الْمَكَانِ يَقُولُ أُنْزِلَتْ هَذِهِ الآيَةُ { وَمَنْ يَقْتُلْ مُؤْمِنًا مُتَعَمِّدًا فَجَزَاؤُهُ جَهَنَّمُ خَالِدًا فِيهَا } بَعْدَ الَّتِي فِي الْفُرْقَانِ { وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ وَلاَ يَقْتُلُونَ النَّفْسَ الَّتِي حَرَّمَ اللَّهُ إِلاَّ بِالْحَقِّ } بِسِتَّةِ أَشْهُرٍ