Chapter 37: The Book of Fighting [The Prohibition of Bloodshed]
It was narrated from Abu Hurairah that: The Messenger of Allah [SAW] said: "We will fight the people until they say La ilaha illallah. If they say La ilaha illallah then their blood and their wealth become forbidden to us, except for a right that is due, and their reckoning will be with Allah."
Sunan an-Nasa'i 3978