Today, ṣadaqa is commonly defined as voluntary alms, and zakāt as obligatory alms. However, their nature was totally different in the time of the prophet Muḥammad; zakāt was always a form of voluntary alms, while conversely, ṣadaqa in Muḥammad’s last years was a compulsory tax levied especially for the expenditure of jihād. Early Muslim scholars, particularly in Arabia and Iraq, had disliked the tax due to the central government and endeavoured for a long period to exclude from ṣadaqa the nature as a tax due. I will investigate below the process how ṣadaqa changed by nature in the early Islamic period.