The intrigues of the Turks in Baghdad increased with the help of the chamberlain. In the year 245 AH, Musa bin Waṣif, one of the killers of al-Mutawakkil, ordered that al-Mu'tazz be deposed and replaced by al-Musta'in. In that year, al-Mu'tazz abdicated and was imprisoned for four years. He only ruled for a short period. They cut off his food, and he starved after six days. They appointed his cousin, al-Musta'in, in his place. Al-Musta'in was the son of al-Wathiq and was twenty-five years old.

On Wednesday, the twenty-seventh of Rajab of this year, Muhammad bin al-Wathiq was pledged allegiance to as caliph and was given the title al-Muhtadi Billah. His kunya was Abu Abdullah, and his mother was Qabiḥa. In Ramadan of this year, Qabiḥa, the mother of al-Mu'tazz, appeared. She had been in hiding since her son was killed. Qabiḥa had great wealth in Baghdad, estimated at one million dinars, which was found in a chest of emeralds, another chest of rubies, and a chest of unparalleled red sapphires. All of this was brought to Ṣāliḥ bin Waṣif. Ṣāliḥ said, "May God curse Qabiḥa. She bore two sons, and they were killed for the sake of one hundred thousand dinars, while she had all this wealth." Al-Mutawakkil had named her Qabiḥa because of her beauty. Her son was called al-Mu'tazz. Then she began to call out loudly against Ṣāliḥ bin Waṣif, saying, "You have violated my honor, killed my son, taken my wealth, exiled me from my land, and committed great indecency."

Al-Musta'in and his death. Muhammad al-Muhtadi bin Harun al-Wathiq bin al-Mu'tasim died on the twenty-seventh of Rajab in the year 256 AH, twelve nights before the end of the month. The reason for his death was that he intended to kill Musa bin Bugha. Musa bin Bugha was encamped opposite some of the border regions. He wrote to Ba'ikiyal, who was one of the Turkish leaders, to kill Musa bin Bugha and take his place. Ba'ikiyal agreed to this. They conspired to kill al-Muhtadi. Ba'ikiyal went to Samarra and entered the palace. Al-Muhtadi intended to kill him, but Ba'ikiyal killed him instead. When al-Muhtadi went to fight Musa, the Turks who were with al-Muhtadi abandoned him and joined their fellow Turks with Musa. Al-Muhtadi was weakened, fled, and entered the palace. He remained there for twenty-four days and was buried in the cemetery of the palace. Al-Muhtadi's caliphate lasted for eleven and a half months. He was thirty-two years old. His son was in al-Qāṭūl. He was pious and devoted to worship. He intended to be like Umar bin Abdul Aziz among the Abbasids, as Umar bin Abdul Aziz was among the Umayyads.