أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا شَرِيكٌ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَامِرٍ، عَنْ جَرِيرٍ، قَالَ أَيُّمَا عَبْدٍ أَبَقَ مِنْ مَوَالِيهِ وَلَحِقَ بِالْعَدُوِّ فَقَدْ أَحَلَّ بِنَفْسِهِ ‏.‏

It was narrated that Jarir said: "Any slave who runs away from his masters and joins the enemy, he has made it permissible to shed his blood." Translation Not Available

Book Ref: Sunan An Nisai Book 37 Hadith 4056
Web Ref:  Sunan An Nisai Vol 5 Book 37 Hadith 4061