This forum is to be used for all discussions pertaining to Bethesda Softworks' The Elder Scrolls III: Morrowind and its Tribunal and Bloodmoon expansion packs.
Actually, I was attacked by the assassin while sleeping inside Ra'Virr's house in Balmora, If that's his name, And in my other file I was sleeping in Nine-Toes' house. You do not need to be sleeping in the wilderness for this to happen.
Stating the obvious, you need Tribunal to trigger the assassination.
And where you sleep doesn't matter in any way. You can sleep on top of one of the Vivec Cantons if you feel like it and still get attacked...
and your lvl doesn't affect either, i usually get some steel armour walk outside of seyda neen and sleep until i get attacked, kill the assassin take the stuff and i do that at lvl 1 and it always works, it sounds to me that as Rane says, do you have tribunal installed??