Zakat is obligatory upon Muslims
Allah the Exalted said: (And perform As-Salat, and give Zakat (Obligatory Charity)) (The Noble Qur’an 2:43) The hadith of Ibn Abbas that the Prophet told Mu’aadh when he sent him to Yemen: (Inform them that Allah prescribed upon them charity to be taken from their rich and given to their poor) (Al-Bukhari & Muslim)
If a rich man says to you: “I’ll give you 40,000 Riyals, but you must give 1000 of it in charity”. Will you accept his offer? Is it wise not to accept it?! Well, to Allah belongs the highest attribute; Allah the one who provides has placed rules to show appreciation for his provision; and giving Zakat is amongst that.