We Muslims are giving zakat every year and we know it is obligatory. One of my friend questioned why we have to give every year, where it is written? As per him, it is once in a life. Please give the evidence from Quran and Hadith for supporting that zakat has to be given on yearly basis.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Over the last fourteen centuries, the Muslims have not differed over the fact that the Zakah (obligatory alms) must be paid every lunar year if it fulfils the conditions of Zakah. Moreover, the scholars did not differ about this issue until some ignorant people like your friend came up with the view that Zakah is only obligatory once in a lifetime.

The Prophet said: "There shall come deceptive years. The truthful shall be deemed liars, while the liars shall be believed. The honest shall be deemed dishonest, while the dishonest shall be deemed honest. (And) the Ruwaybidhah will speak in those times." The Companions asked, "What is a Ruwaybidhah O Messenger of Allah?" He replied: "It is an insignificant man who shall speak on behalf of the general masses." [Ahmad and Ibn Maajah]

Therefore, the above narration applies to people like your friend, and the term "Ruwaybidhah" applies to these ignorant people who speak about important matters of the Muslims.

Indeed, there is evidence from the Book of Allah, the Sunnah of the Prophet and the consensus of the scholars  that Zakah must be paid every year.

Allah says about the Zakah on crops (what means): {And pay the due thereof (its Zakah, according to Allah's Orders) on the day of its harvest.} [Quran 6:141]

It is also confirmed that the Prophet  said: "If a person does three things, he will indeed find the sweetness of faith: (1) If he worships Allah alone without associating with Him any partners and knows that none has the right to be worshipped but Allah, and (2) Pays the Zakat of his wealth as a purification for himself to be enabled to pay it every year….. " [Abu Daawood]

Ibn Hazm said, "The Zakah must be paid every year for camels, cows, sheep (and goats), and gold and silver (currencies),…and there is no difference of opinion among the scholars about this at all."

Therefore, your friend should stop issuing Fatwas and speaking about issues of the religion of Allah without knowledge, and he should seek Allah's forgiveness and repent to Him before he dies.

For more, please refer to fatwas 85709 and 87401.

Allah knows best.