Bulugh al-Maram 604

Bahz bin Hakam narrated on the authority of his father, who reported on the authority of his grandfather (RAA) that the Messenger of Allah (ﷺ) said: “For every forty camels, one ‘bint labun’ (a young female camel which is two years old and already starting the third year), is due as Zakah. No camel is to be separated from the rest of the camels (i.e. the jointly owned live stock as mentioned above). Whoever gives it willingly, seeking his reward from Allah, will be rewarded. (However) if someone refrains from paying it, it will be taken from him (by force) along with part of his property (as punishment), for it is a right of Allah. None of it is lawful for the family of Muhammad (ﷺ)." Related by Ahmad, An-Nasa’i, Abu Dawud and Al-Hakim rendered it Sahih. And Ash-Shafi'ee conditioned ruling by it depending on its authenticity.