(1) باب وُجُوبِ الْجِهَادِ .
Narrated It was narrated that Ibn Abbas said:
"When the Prophet was expelled from Makkah, Abu Bakr said to him: 'They have driven out their Prophet, verily to Allah we belong and to Him we return. They are surely doomed.' Then it was revealed: 'Permission to fight (against disbelievers) is given to those (believers) who are fought against, because they have been wronged; and surely, Allah is able to give them (believers) victory.' Then I knew that there would be fighting." Ibn Abbas said: "This is the first Verse that was revealed concerning fighting."
Reference: Sunan an-Nasa'i 3085
In-book reference: Book 25, Hadith 1
English translation: Vol. 1, Book 25, Hadith 3087