Muhammad bin Abi Da'ud al-Bghdady محمد بن أبي داود · Jihad (Kitab Al-Jihad)

The Prophet (ﷺ) said: Striving in the path of Allah (jihad) is incumbent on you along with every ruler, whether he is pious or impious; the prayer is obligatory on you behind every believer, pious or impious, even if he commits grave sins; the (funeral) prayer is incumbent upon every Muslim, pious and impious, even if he commits major sins.

The Prophet (ﷺ) said: The best number of companions is four, the best number in expeditions four hundred, and the best number in armies four thousand; and twelve thousand will not be overcome through smallness of numbers. Abu Dawud said: What is correct is that this tradition is mursal (i.e. the link of the Companion is missing).

Nafi' said that a slave of Ibn Umar ran away to the enemy, and then the Muslims overpowered them. The Messenger of Allah (ﷺ) returned him to Ibn Umar and that was not distributed (as a part of booty). Abu Dawud said: The other narrators said: Khalid b. al-Walid returned him to him (Ibd 'Umar).