Who among the four rightly guided caliphs introduced the systems of Bayr at māl?

The system of Bayt al-Māl was introduced by the second Caliph of Islam, 'Umar ibn al-Khattab (may Allah be pleased with him). Bayt al-Mal is the treasury of the Islamic state where money, land, and other valuable items are collected for the betterment of the community. After the death of the first caliph, Abu Bakr (may Allah be pleased with him), 'Umar (may Allah be pleased with him) became the caliph and established the system of Bayt al-Mal to manage the financial affairs of the Muslim community. The Bayt al-Mal system was intended to ensure the equitable distribution of resources among Muslims, particularly the poor and needy. It was also used to support the building of mosques, schools, and hospitals. Therefore, it was 'Umar (may Allah be pleased with him) who introduced the system of Bayt al-Mal in the early days of Islam and played an essential role in establishing it as a key institution of the Muslim community.