Sunan an-Nasa'i 3969
سنن النسائي#3969SahihIt was narrated that Anas bin Malik said:"When the Messenger of Allah [SAW] died, the 'Arabs apostatized, so 'Umar said: 'O Abu Bakr, how can you fight the 'Arabs?' Abu Bakr said: 'The Messenger of Allah [SAW] said: "I have been commanded to fight the people until they bear witness to La ilaha illallah (there is none worthy of worship except Allah) and that I am the Messenger of Allah, and they establish Salah and pay Zakah." By Allah, if they withhold from me a young goat that they used to give to the Messenger of Allah [SAW], I will fight them for it.' 'Umar said: 'By Allah, as soon as I realized how certain Abu Bakr was, I knew that it was the truth
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
In-book reference: 37:4