Muhammadite Shia
The Muhammadite Shia (named for Muhammad al Askari ibn Imam Ali al-Hadi) were a Shia sect who believed that due to the supposed lack of a son (according to their opinion) for Hasan al-Askari, they had to rethink the legitimacy of his Imamate. Therefore, they instead believed in the Imamate of his brother Muhammad al Askari ibn Imam Ali al-Hadi, who died 7 years before the death of his father.