The Prophet ﷺ sent Muaz to Yemen and said, "You are going to a people of the Book. Call them to testify that there is no god but Allah and that I am the Messenger of Allah. If they obey you in that, then inform them that Allah has made obligatory upon them five prayers in every day and night. If they obey you in that, then inform them that Allah has made obligatory upon them a charity to be taken from their wealth, taken from their rich and given back to their poor. If they obey you in that, then beware of taking the most prized portions of their wealth, and beware the supplication of the wronged, for there is no barrier between it and Allah."
حدثنا علي بن محمد حدثنا وكيع بن الجراح حدثنا زكريا بن إسحق المكي عن يحيى بن عبد الله بن صيفي عن أبي معبد مولى ابن عباس
أن النبي ﷺ بعث معاذا إلى اليمن فقال إنك تأتي قوما أهل كتاب فادعهم إلى شهادة أن لا إله إلا الله وأني رسول الله فإن هم أطاعوا لذلك فأعلمهم أن الله افترض عليهم خمس صلوات في كل يوم وليلة فإن هم أطاعوا لذلك فأعلمهم أن الله افترض عليهم صدقة في أموالهم تؤخذ من أغنيائهم فترد في فقرائهم فإن هم أطاعوا لذلك فإياك وكرائم أموالهم واتق دعوة المظلوم فإنها ليس بينها وبين الله حجاب
Bukhari narrated it in the Book of Injustices, in the chapter on being wary and cautious of the supplication of the wronged, hadith no. 2448, abridged, from the hadith of Waki, see also hadith no. 1395, and elsewhere, and Muslim, in the Book of Faith, in the chapter on inviting people to the two testimonies of faith and the laws of Islam, hadith no. 19, from the hadith of Waki, with the same chain.