of apostasy and, ultimately, the Ridda wars. The second and third caliphs, Umar ibn al-Khattab and Usman ibn Affan, continued Abu Bakr's codification of the zakat. Uthman also modified the zakat collection protocol by decreeing that only "apparent" wealth was taxable, which had the effect of limiting zakat to mostly being paid on agricultural land and produce. During the reign of Ali ibn Abu Talib, the issue of zakat was tied to legitimacy of his government. After Ali, his supporters refused to pay zakat to Muawiyah I, as they did not recognize his legitimacy. The practice of Islamic state-administered zakat was short-lived in Medina. During the reign of Umar bin Abdul Aziz (717–720 AD), it is reported that no one in Medina needed the zakat. After him, zakat came more to be considered as an individual responsibility. This view changed over Islamic history. Sunni Muslims and rulers, for example, considered collection and disbursement of zakat as one of the functions of an Islamic state; this view has continued in modern Islamic countries. Zakat is one of the five pillars of Islam, and in various Islamic polities of the past was expected to be paid by all practising Muslims who have the financial means (nisab). In addition to their zakat obligations, Muslims were encouraged to make voluntary contributions (sadaqat). The zakat was not collected from non-Muslims, although they were required to pay the jizyah tax. Depending on the region, the dominant portion of zakat went typically to Amil (the zakat collectors) or Sabīlillāh (those fighting for religious cause, the caretaker of local mosque, or those working in the cause of God such as proselytizing non-Muslims to convert to Islam). Contemporary practice According to the researcher Russell Powell in 2010, zakat was mandatory by state law in Libya, Malaysia, Pakistan, Saudi Arabia, Sudan, and Yemen. There were government-run voluntary zakat contribution programs in Bahrain, Bangladesh, Egypt, Indonesia, Iran, Jordan, Kuwait, Lebanon, Maldives and the United Arab Emirates. In a 2019 study conducted by the Institute for Social Policy and Understanding that examined philanthropy for American Muslims in comparison to other faith and non-faith groups, it was found that for American Muslims, Zakat was an important driver of charitable giving. This results in American Muslims being the most likely faith group studied to be motivated to donate based on a believed religious obligation (zakat), and a “feeling that those with more should help