Obviously, the Prophet (peace be upon him) would have been the first to comply with any command he issued. He said: “Certainly by Allah, I am the most God-fearing among you.” [Sahîh Muslim]
However, Zakâh is not obligatory on every individual. There are conditions that make people liable to pay. The first condition is that the person possesses a certain minimum amount of wealth that makes Zakâh obligatory. The second is that the person holds this amount in savings for a full year.
These conditions never existed for the Prophet (peace be upon him). His life was so simple that he lived on a day-to-day subsistence income. Take the following illustrative example:
`Aishah told her nephew `Urwah: “By Allah, my nephew, we would go two out of three months without without having any fire for cooking in all of the Prophet’s (peace be upon him) houses.”
`Urwah asked her: Then how did you survive, my Aunt?”
She said: “On dates and water.” [Sahîh Muslim]
The Prophet (peace be upon him) died while his shield was held in mortgage by a Jew. He pawned his shield so he could purchase food.
The Prophet (peace be upon him) did order his family members to pay Zakâh.
One time he came to `Aishah while she was holding some silver rings. He said: “What is that O `Aishah?”
She said: I made them to beautify myself for you, O Messenger of Allah.
He said: “Do you pay Zakâh for them?” When she replied that she had not, he said: “Then they are your share of the Fire.”
In brief, we would say that the Prophet (peace be upon him) is equally obliged by Islam's commands or prohibitions, save for a few rulings that applied only to him, such as the permission to marry more than four wives, the obligation of praying the Tahajjud prayer, and his fasting consecutive days without breaking his fast at night.
Source: Islam Today