A force was now being prepared under Usama, Ibn Zaid, whose father was killed at Muta, against the Byzantines, to exact the long-delayed reparation for the murder of the envoy to Syria. However, the news of the Prophet's sickness and failing health caused that expedition to be stopped. This news was soon noised abroad and produced disorder in some districts. Three pretenders had arisen who gave themselves out as prophets and tried by all kinds of imposture to win over their tribes. The most dangerous of these pretenders was known as Al Aswad. He was a chief of Yemen and a man of great wealth and sagacity, as well as a clever conjurer. He soon succeeded in gaining over his tribesmen and, with their help, reduced to subjection many of the neighboring towns. He killed Shahr, whom the Prophet had appointed as Governor of Sana in the place of his father Bazan, who had just died. Bazan had been the viceroy of Yemen under Chosroes of Persia; after he had adopted Islam he was allowed by the Prophet to remain as Governor of Yemen. He was able to convert to Islam all the Persian colony in that province. Al-Aswad, the conjurer, had now killed Shahr, but soon after he was massacred by the Persians of Yemen.

The other two pretenders, Tulayha and Haroun by name, were not suppressed until after the death of the Prophet, during the reign of Abu Bakr. Haroun, better known as Mussaylamah, addressed to the Prophet a letter which ran as follows: "From Mussaylamah the Prophet of Allah, to Muhammad the Prophet of Allah. Peace be to you. I am your partner. Let the exercise of authority be divided between us. Half the earth will be mine, and half will belong to your Quraish. But the Quraish are too greedy to be satisfied with a just division." To this letter the Prophet replied as follows: "From Muhammad the Messenger of Allah, to Mussaylamah the liar. Peace be to those who follow the right path. The earth belongs to Allah. It is He Who makes to reign whomsoever He pleases. Only those will prosper who fear the Lord."