Obligation of Zakah
The importance of Zakah is emphasised to such a degree in Islam that Allah (سبحانه و تعالى) mentions it with Salah, the prayer in 30 verses of the Quran. Zakagh is an obligatory pillar of Islam and it was first revealed in Surah Al Muzzamil where Allah (سبحانه و تعالى) compares it to giving a loan to Allah (سبحانه و تعالى):
".... So recite as much of the Quran as may be easy (for you), and perform As-Salat (Iqamat-as-Salat) and give Zakat, and lend to Allah a goodly loan, and whatever good you send before you for yourselves, (i.e. Nawafil non-obligatory acts of worship: prayers, charity, fasting, Hajj and 'Umrah, etc.), you will certainly find it with Allah, better and greater in reward. And seek Forgiveness of Allah. Verily, Allah is Oft-Forgiving, Most-Merciful." [Quran: Surah al Muzzamil 73: Ayah 20]
And His statement: "Take Sadaqah (alms) from their wealth in order to purify them and sanctify them with it, and invoke Allah for them. Verily! Your invocations are a source of security for them, and Allah is All-Hearer, All-Knower." [Quran: Surat At-Tawbah 9: Ayah103]
And: "O you who believe! Spend of the good things which you have (legally) earned, and of that which We have produced from the earth for you..." [Quran: Surat al Baqarah 2: Ayah 267]
In another Ayah, Allah (سبحانه و تعالى) declares that those that are astray but repent, establish the prayer and who give Zakah, are included within the brotherhood of the Muslims:
"But if they repent, perform As-Salat (Iqamat-as-Salat) and give Zakat, then they are your brethren in religion. (In this way) We explain the Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.) in detail for a people who know." [Quran: Surah at Tawbah 9: Ayah 11]
The obligation of Zakah can be found in the statement of the Messenger (صلى الله عليه و سلم): "lslam was built upon five (pillars): The testimony that none has the right to be worshipped hut Allah and Muhammad is the Messenger of Allah, the establishment of the prayer (Salah), paying the obligatory charity (Zakah), pilgrimage to the House (Hajj to the Ka’bah in Makkah) and fasting (the month of) Ramadhan.)" [Al-Bukhari and Muslim]
It is related on the authority of Ibn `Abbas (رضی اللہ عنہ) that the Messenger of God (صلى الله عليه و سلم) sent Mu`adh to the Yemen he told him, "You are going to a people who have a Scripture, so call them to testify that there is no deity but God, and that I am the Messenger of God. If they respond to this, then teach them that God has imposed five Salats upon them in every day. If they respond to this, then teach them that God has imposed upon them a charity to be taken from the wealthy amongst them and given to their poor. If they respond to this, then beware of taking any more of their wealth! Beware also of the prayer of the oppressed, for there is no veil between such a prayer and God."[Al-Bukhari and Muslim]
When was Zakah Made Obligatory?
There seems to be some difference of opinion as to when the Zakah was made obligatory upon the Muslims. The concensus appears to be that became an obligatory duty in Makkah before the Hijrah, migration to Madeenah, then from 2AH, after the Hijrah, the definition of the rates and the detailed rulings were established.
Ibn Katheer (رحمه الله) wrote: It is not far-fetched to say that the principle of obligatory charity (zakah) was enjoined at the beginning of the Prophet’s mission, as in the verse: “but pay the due thereof on the day of their harvest” [al-An‘aam 6:141]. As for the zakah in which there is a minimum threshold and set rates, that was introduced in Madeenah. He also mentioned that "the obligation of zakah came in the second year AH in Madeenah, according to what was stated by more than one." [Tafseer Ibn Katheer, 7/164]
Al-Haytami (رحمه الله) said in Tuhfat al-Muhraaj (3/209): The obligation to pay zakah on one’s wealth came in the second year AH, after sadaqat al-fitr was introduced.
Shaykh Ibn ‘Uthaymeen (رحمه الله) said: Zakah was enjoined, according to the soundest opinion of the scholars, in Makkah, but the definition of the minimum threshold and types of wealth on which zakah is due, and who is entitled to zakah, came in Madeenah. End quote. [Majmoo‘ Fataawa Ibn ‘Uthaymeen, 13/1357]