سنن النسائي

It was narrated from Ibn 'Abbas that the Prophet (ﷺ) sent Mu'adh bin Jabal to Yemen and said: "You are going to some people from among the people of the Book. Call them to bear witness that there is none worthy of worship except Allah and that I am the Messenger of Allah. If they obey you in that, then teach them that Allah has enjoined upon them five prayers every day and night. If they obey you in that, then teach them that Allah has enjoined upon them Sadaqah (Zakah) from their wealth, to be taken from their rich and given to their poor. If they obey you in that, then do not touch the most precious of their wealth, and fear the supplication of the one who has been wronged, for there is no barrier between it and Allah, the Mighty and Sublime."