When the Prophet ﷺ sent Muʿadh 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." (Using translation from Bukhārī 7372)   

عَبَّاسٍ ؓ يَقُولُ لَمَّا بَعَثَ رَسُولُ اللهِ ﷺ مُعَاذَ بْنَ جَبَلٍ نَحْوَ الْيَمَنِ فَقَالَ إِنَّكَ تَقْدَمُ عَلَى قَوْمٍ مِنْ أَهْلِ الْكِتَابِ فَلْيَكُنْ أَوَّلَ مَا تَدْعُوهُمْ أَنْ يُوَحِّدُوا اللهَ ﷻ فَإِذَا عَرَفُوا ذَلِكَ فَأَخْبِرْهُمْ أَنَّ اللهَ ﷻ قَدِ افْتَرَضَ عَلَيْهِمْ خَمْسَ صَلَوَاتٍ فِي يَوْمِهِمْ وَلَيْلَتِهِمْ فَإِذَا صَلَّوْا فَأَخْبِرْهُمْ أَنَّ اللهَ ﷻ قَدِ افْتَرَضَ عَلَيْهِمْ زَكَاةً فِي أَمْوَالِهِمْ تُؤْخَذُ مِنْ غَنِيِّهِمْ فَتُرَدُّ عَلَى فَقِيرِهِمْ فَإِذَا أَقَرُّوا بِذَلِكَ فَخُذْ مِنْهُمْ وَتَوَقَّ كَرَائِمَ أَمْوَالِهِمْ