When the Messenger of Allah ﷺ sent Muaz to Yemen, he said to him, "You are going to a people who are People of the Book. Let the first thing you call them to be the worship of Allah. Once they recognize Allah, inform them that Allah has made five prayers obligatory upon them in each day and night. When they have done so, inform them that Allah has made zakat obligatory upon them from their wealth, to be taken from their rich and given back to their poor. If they comply with that, then take from them, but avoid the most prized portions of their wealth."
أن رسول الله ﷺ لما بعث معاذا على اليمن قال: إنك تقدم على قوم أهل الكتاب فليكن أول ما تدعوهم إليه عبادة الله، فإذا عرفوا الله فأخبرهم أن الله قد فرض عليهم خمس صلوات في يومهم وليلتهم، فإذا فعلوا فأخبرهم أن الله فرض عليهم زكاة من أموالهم، وترد على فقرائهم، فإذا أطاعوا بها فخذ منهم وتوق كرائم أموالهم.
Bukhari narrated it in the Book of Zakat (1458), and Muslim in the Book of Faith (19), both from Umaya bin Bistam, from Yazid bin Zuray, from Ismail bin Umaya, from Yahya bin Abdullah bin Muhammad Sayfi, that he heard Abu Mabad, the freed slave of Ibn Abbas, say, I heard Ibn Abbas say, and then he mentioned it.