أَخْبَرَنَا أَحْمَدُ بْنُ حَفْصِ بْنِ عَبْدِ اللَّهِ، قَالَ حَدَّثَنِي أَبِي قَالَ، حَدَّثَنِي إِبْرَاهِيمُ، عَنْ عَبْدِ الْعَزِيزِ بْنِ رُفَيْعٍ، عَنْ عُبَيْدِ بْنِ عُمَيْرٍ، عَنْ عَائِشَةَ أُمِّ الْمُؤْمِنِينَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ قَالَ ‏"‏ لاَ يَحِلُّ قَتْلُ مُسْلِمٍ إِلاَّ فِي إِحْدَى ثَلاَثِ خِصَالٍ زَانٍ مُحْصَنٍ فَيُرْجَمُ وَرَجُلٌ يَقْتُلُ مُسْلِمًا مُتَعَمِّدًا وَرَجُلٌ يَخْرُجُ مِنَ الإِسْلاَمِ فَيُحَارِبُ اللَّهَ عَزَّ وَجَلَّ وَرَسُولَهُ فَيُقْتَلُ أَوْ يُصَلَّبُ أَوْ يُنْفَى مِنَ الأَرْضِ ‏"‏ ‏.‏

It was narrated from 'Aishah, the Mother of the Believers, that the Messenger of Allah said: "It is not permissible to kill a Muslim except in one of three cases: A adulterer who has been married, who is to be stoned; a man who kills a Muslim deliberately; and a man who leaves Islam and wages war against Allah, the Mighty and Sublime, and His Messenger, who is to be killed, crucified or banished from the land." Translation Not Available

Book reference: Sunan An Nisai Book 45 Hadith 4743
Web reference: Sunan An Nisai Volume 5 Book 45 Hadith 4747