 When he had signed away his rights to the caliphate in 862, he had been under duress to do so, with the Turks threatening to kill him if he refused, and therefore he considered the deed of abdication to be void.He also sought to convince the people that they could switch their allegiance to him without breaking the oath they had taken to serve al-Musta'in, and went through the effort to explain in detail how this could be done in a letter to Muhammad b.