Sunan an-Nasa'i 3978
سنن النسائي#3978SahihIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahHasan Sahih
Al-AlbaniHasan Sahih
Zubair Ali ZaiSahih
In-book reference: 37:13