Abdullah bin Abbas (may Allah be pleased with them both) narrates: When the Prophet (peace and blessings of Allah be upon him) sent Mu’adh (may Allah be pleased with him) to Yemen, he said:“You are going to a people of the Book, so call them to testify that there is no deity except Allah and that I am the Messenger of Allah. If they obey you in this, then inform them that Allah has enjoined upon them five prayers every day and night. If they obey you in this, then inform them that Allah has made charity obligatory upon them, to be taken from their wealthy and given to their poor. If they accept this from you, then avoid taking the best of their wealth, and beware of the supplication of the oppressed, for there is no barrier between it and Allah.”