Sunan an-Nasa'i, Volume 5, Book 37, Hadith 4057 (DarusSalam) ⓘ
It was narrated that Jarir said: "The Messenger of Allah [SAW] said: 'If a slave runs away to the land of Shirk, it becomes permissible to shed his blood.'"
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حُمَيْدُ بْنُ عَبْدِ الرَّحْمَنِ، عَنْ أَبِيهِ، عَنْ أَبِي إِسْحَاقَ، عَنِ الشَّعْبِيِّ، عَنْ جَرِيرٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا أَبَقَ الْعَبْدُ إِلَى أَرْضِ الشِّرْكِ فَقَدْ حَلَّ دَمُهُ " .
also referenced under: Hadith 4052 (Reference) & Book 37, Hadith 87 (In-Book)