The Sadaqat which represent a revenue for the Bait ul-Mal is the Zakat. Sadaqah when mentioned generally means Zakat, and Zakat when mentioned generally means Sadaqah. Zakat linguistically means the increase, and it also means the purification. It is present in the Shar’a with both meanings because giving Zakat is a cause of blessing for wealth due to the Hadith: “The property of a person (‘Abd) does not decrease because of Sadaqah,” or reward increases because of it. It also purifies the soul from stinginess and it is a purification of sins.
It is defined in the Shar’a as a determined right due from certain types of wealth. It is one of the worships (‘Ibadat) and a basic element (Rukn) of Islam like prayer, fasting and Hajj. Zakat is obliged upon Muslims only, and is not taken from others. It’s obligation is established by the Book and Sunnah. Allah (swt) says: “Give the Zakat” [Al-Muzzammil: 20]
The Prophet (saw) sent Mu’az to Yemen and said to him: “Inform them that Allah obliged Sadaqah upon their wealth that is taken from their rich and given to their poor.” Harsh punishments are promised to those who prevent and withhold the Zakat. Abu Hurayra narrated that the Prophet (saw) said: “No owner of gold or silver who fails to give its due right except that he will have sheets of fire made for him on the Day of Judgement.
They will be heated in the Hellfire then used to burn his sides, forehead and back. Whenever they cool, they are reheated to him in a Day which is 50,000 years long, until it is judged between the people and he is shown his path, either to Paradise or to the Fire.” It was said:
‘O Messenger of Allah, what of the camels?’ He said: “No owner of camels who fails to give their due right, and of their right is their milk the day they reach water, except that on the Day of Judgement a level plain will be extended for camels as most plentiful without one young camel been lost. They will trample him with their feet and bite him with their mouths. As soon as the first one passes him the last one will return in a Day which is 50,000 years long, until it is judged between the people and he is shown his path, either to Paradise or to the Fire.” It was said: ‘O Messenger of Allah, what of the cows and sheep?’ He said: “No owner of cows or sheep who fails to give their due right, except that on the Day of judgement a level plain will be extended for the cows and sheep, without anyone of them being lost whether a rebellious one, or of broken horn or of scanty hair on head. They will butt him with their horns and trample him with their cloven hoofs.
As soon as the first one passes by the last one will return in a Day which is 50,000 years long, until it is judged between the people. Then he will be shown his path, either to Paradise or the Fire.” (narrated by the five except At-Tirmizi)
The Zakat is a personal duty (Fardh ‘Ayn) on every Muslim who possesses the minimum amount (Nisab) in excess of his debts for the duration of a year. Whenever it becomes obligatory upon the wealth of a Muslim, it cannot be abolished. Its collection is independent of the State’s needs or the Ummah’s interests unlike the tax funds, which might be collected from the Ummah only in cases where there are no funds in the Bait ul-Mal to meet the State’s needs and the Ummah’s interests. Rather it is the right of the eight categories that the State must deliver to the Bait ul-Mal whenever it becomes due, whether there is a need for it or not. Zakat is not of the rights of the Bait ul-Mal nor is it a beneficiary from it. It is a right of the eight categories specified by Allah (swt) in the Ayah: “Verily the Sadaqah is only for…” [At-Tauba: 60]
The Bait ul-Mal is only a place of sanctuary for it, such that the Imam will spend from it to those specified by the Ayah according to his view and Ijtihad.
Zakat is obliged upon the man, woman, child and insane person due to the general form of the sound Ahadith that oblige Zakat without restriction.
Amru bin Shu’aib narrated from his father from his grandfather he said: “The Prophet (saw) preached to the people and said: ‘Verily, whoever has charge over an orphan with wealth then let him invest it. He should not leave it to be eaten by Sadaqah.’” From Anas (in a Marfu’ narration): “Trade in the orphans’ wealth (so that) Zakat does not consume it.”
Qasim bin Muhammad said: “Aisha used to invest our wealth, as we were orphans, and give Zakat from it.” Malik bin Anas considered that there was Zakat on the lunatic’s wealth, as did Az-Zuhri. From ibn Shihab: “That he  was asked about the lunatic’s wealth, is there Zakat upon it? He  said: ‘Yes.’”
Zakat is obliged on the following properties:
1. Livestock including camels, cows and sheep,
2. Crops and fruits,
4. Trading goods and merchandise.
Zakat is obliged on these properties if they reach the Nisab for the duration of one year except for crops and fruits whose Zakat is due the moment they are harvested.