Troubles emerged soon after Muhammad's death, threatening the unity and stability of the new community and state. Apostasy spread to every tribe in the Arabian Peninsula with the exception of the people in Mecca and Medina, the Banu Thaqif in Ta'if and the Bani Abdul Qais of Oman. In some cases, entire tribes apostatised. Others merely withheld zakat, the alms tax, without formally challenging Islam. Many tribal leaders made claims to prophethood; some made it during the lifetime of Muhammad. The first incident of apostasy was fought and concluded while Muhammad still lived; a supposed prophet Aswad Ansi arose and invaded South Arabia; he was killed on 30 May 632 (6 Rabi' al-Awwal, 11 Hijri) by Governor Fērōz of Yemen, a Persian Muslim. The news of his death reached Medina shortly after the death of Muhammad. The apostasy of al-Yamama was led by another supposed prophet, Musaylimah, who arose before Muhammad's death; other centers of the rebels were in the Najd, Eastern Arabia (known then as "al-Bahrayn") and South Arabia (known as "al-Yaman" and including the "Mahra"). Many tribes claimed that they had submitted to Muhammad and that with Muhammad's death, their allegiance was ended. Caliph Abu Bakr insisted that they had not just submitted to a leader but joined an "ummah" (, community) of which he was the new head. The result of this situation was the Ridda wars.