Sunan an-Nasa'i 3972
سنن النسائي#3972SahihAbu Hurairah narrated that :The Messenger of Allah [SAW] said: "I have been commanded to fight the people until they say La ilaha illallah (there is none worthy of worship but Allah). Whoever says La ilaha illallah, his wealth and his life are safe from me except for a right that is due, and his 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 GhuddahSahih Mutawatir
Al-AlbaniSahih Mutawatir
Zubair Ali ZaiHasan
In-book reference: 37:7