Riyad as-Salihin 208

Mu'adh (May Allah bepleased with him) reported that Messenger of Allah (ﷺ) sent me (as a governor of Yemen) and instructed me thus: "You will go to the people of the Book. First call them to testify that 'there is no true god except Allah, that I am (Muhammad (ﷺ)) the Messenger of Allah.' If they obey you, tell them that Allah has enjoined upon them five Salat (prayers) during the day and night; and if they obey you, inform them that Allah has made Zakat obligatory upon them; that it should be collected from their rich and distributed among their poor; and if they obey you refrain from picking up (as a share of Zakat) the best of their wealth. Beware of the supplication of the oppressed, for there is no barrier between it and Allah". [Al-Bukhari and Muslim].