"‏ إِنَّكَ تَقْدَمُ عَلَى قَوْمٍ مِنْ أَهْلِ الْكِتَابِ فَلْيَكُنْ أَوَّلَ مَا تَدْعُوهُمْ إِلَى أَنْ يُوَحِّدُوا اللَّهَ تَعَالَى فَإِذَا عَرَفُوا ذَلِكَ فَأَخْبِرْهُمْ أَنَّ اللَّهَ فَرَضَ عَلَيْهِمْ خَمْسَ صَلَوَاتٍ فِي يَوْمِهِمْ وَلَيْلَتِهِمْ، فَإِذَا صَلُّوا فَأَخْبِرْهُمْ أَنَّ اللَّهَ افْتَرَضَ عَلَيْهِمْ زَكَاةً فِي أَمْوَالِهِمْ تُؤْخَذُ مِنْ غَنِيِّهِمْ فَتُرَدُّ عَلَى فَقِيرِهِمْ، فَإِذَا أَقَرُّوا بِذَلِكَ فَخُذْ مِنْهُمْ وَتَوَقَّ كَرَائِمَ أَمْوَالِ النَّاسِ ‏"

When the Prophet (ﷺ) sent Mu`adh to Yemen, he said to him, "You are going to a nation from the people of the Scripture, so let the first thing to which you will invite them, be the Tauhid of Allah. If they learn that, tell them that Allah has enjoined on them, five prayers to be offered in one day and one night. And if they pray, tell them that Allah has enjoined on them Zakat of their properties and it is to be taken from the rich among them and given to the poor. And if they agree to that, then take from them Zakat but avoid the best property of the people."