Musannaf Ibn Abi Shaybah 10093 — Withholding zakah

Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said: When the Prophet (peace and blessings be upon him) sent me (to Yemen), he said to me: "You are going to a people from the People of the Book, so invite them to testify that there is no god but Allah and to (accept) my messengership. If they accept that, then inform them that Allah Almighty has made five prayers obligatory upon them in every day and night. If they accept that, then inform them that Allah Almighty has made zakah obligatory upon them in their wealth, to be taken from their rich and spent on their poor. If they accept that, then beware of (taking) the best and most valuable of their wealth, and protect yourself from the supplication of the oppressed, for there is no veil between it and Allah Almighty."