Ali held that the people should be taxed according to their capacity. There should be no hardship or coercion in the collection of taxes. The system of taxation should be such that the people paid the taxes voluntarily as a religious obligation. The collectors should not indulge in any act which is not liked by the people. They should not collect anything beyond what is enjoined by law. Taxes should be remitted in the case of famine, failure of crops or any other calamity.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari