It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that when the Messenger of Allah (peace and blessings be upon him) sent Sayyiduna Mu’adh (may Allah be pleased with him) to Yemen, he said to him:“You are going to a people of the Book, so first invite them to testify that there is no deity worthy of worship except Allah and that I am the Messenger of Allah. If they obey you in this matter, then inform them that Allah has made five prayers obligatory upon them in every day and night. If they accept this as well, then teach them that Allah has made zakat obligatory upon their wealth, to be taken from their rich and distributed among their poor. If they agree to this too, then beware of taking the best of their wealth, and beware of the supplication of the oppressed, for there is no barrier between it and Allah.”