Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: When the Prophet Muhammad (peace and blessings be upon him) sent Sayyiduna Mu’adh to Yemen, he said: You are going to a people from among the People of the Book. When you go to them, invite them to testify that there is no deity except Allah and that Muhammad (peace and blessings be upon him) is the Messenger of Allah. If they accept this from you, then inform them that Allah has made five prayers obligatory upon them every day. If they accept this from you, then inform them that Allah has made zakat obligatory upon them, which is to be taken from their wealthy and given back 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 Allah and it.