Short answer
Most scholars say the detailed duty of zakat, with its nisab and rates, was made obligatory in Madinah in the second year after the Hijrah, around the time fasting in Ramadan was prescribed. Giving zakat was already commanded in general terms in Makkah, and its collection was organised later.
Zakat was made fard in Madinah. The Hanafi books, like most historians, place its obligation in the second year after the Hijrah, before the fast of Ramadan was prescribed.
The four schools agree on this.
Explanation
The word zakah appears in verses revealed in Makkah. Surah al-Mu'minun describes the believers as those who are observant of zakah (23:4), and Surah al-Rum praises what you give as zakah seeking the face of Allah (30:39). Scholars explain that in Makkah this meant purifying charity in general, without a set nisab, rate or year.
The detailed obligation came after the Hijrah. Most scholars date it to the second year in Madinah, the same year in which fasting in Ramadan and zakat al-fitr were prescribed. Some sources place the obligation of zakat al-fitr slightly before that of the yearly zakat.
Some historians gave a later date, around the ninth year, because that is when the Prophet ﷺ sent collectors out to the tribes across Arabia. Most scholars answer that this was when collection was organised on a large scale, not when the duty began, since zakat is mentioned among the obligations in events well before then.
The date does not change anything you owe today. The rules of zakat were complete in the Prophet's ﷺ lifetime and are agreed by the four schools. For the duty itself, see what zakat means and who has to pay zakat.
The evidence
Quran, Surah Ar-Room 30:39
وَمَآ ءَاتَيْتُم مِّن رِّبًۭا لِّيَرْبُوَا۟ فِىٓ أَمْوَٰلِ ٱلنَّاسِ فَلَا يَرْبُوا۟ عِندَ ٱللَّهِ ۖ وَمَآ ءَاتَيْتُم مِّن زَكَوٰةٍۢ تُرِيدُونَ وَجْهَ ٱللَّهِ فَأُو۟لَٰٓئِكَ هُمُ ٱلْمُضْعِفُونَ ﴿٣٩﴾
And whatever you give for interest to increase within the wealth of people will not increase with Allah. But what you give in zakah, desiring the countenance of Allah - those are the multipliers.
A Makkan verse that already mentions zakah.
Quran, Surah Al-Muminoon 23:4
وَٱلَّذِينَ هُمْ لِلزَّكَوٰةِ فَٰعِلُونَ ﴿٤﴾
And they who are observant of zakah
Another Makkan verse describing believers as people of zakah.
Where the ruling is recorded
- Radd al-Muhtar, Kitab al-Zakat, opening section. Records that zakat was made obligatory in the second year after the Hijrah.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.