"‏ إِنَّكَ تَأْتِي قَوْمًا أَهْلَ كِتَابٍ فَادْعُهُمْ إِلَى شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنِّي رَسُولُ اللَّهِ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَأَعْلِمْهُمْ أَنَّ اللَّهَ افْتَرَضَ عَلَيْهِمْ خَمْسَ صَلَوَاتٍ فِي الْيَوْمِ وَاللَّيْلَةِ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَأَعْلِمْهُمْ أَنَّ اللَّهَ افْتَرَضَ عَلَيْهِمْ صَدَقَةً فِي أَمْوَالِهِمْ تُؤْخَذُ مِنْ أَغْنِيَائِهِمْ وَتُرَدُّ عَلَى فُقَرَائِهِمْ فَإِنْ هُمْ أَطَاعُوا لِذَلِكَ فَإِيَّاكَ وَكَرَائِمَ أَمْوَالِهِمْ وَاتَّقِ دَعْوَةَ الْمَظْلُومِ فَإِنَّهَا لَيْسَ بَيْنَهَا وَبَيْنَ اللَّهِ حِجَابٌ ‏"

the Messenger of Allah sent Mu'adh to Yemen and said to him: "You are going to a people from the People of the Book, so invite them to testify that none has the right to be worshipped but Allah, and that I am the Messenger of Allah. If they comply with that, then inform them that Allah has made five prayers obligatory upon them in a day and a night. If they comply with that, then inform then that Allah has ordained a charity upon their wealth, which is to be taken from the rich among them and given to the poor among them. If they comply with that, then beware of their most precious wealth, and protect yourself from the supplication of the oppressed, for there is no barrier between it and Allah."