Muḥammad ibn Zayd ibn Muḥammad ibn Ismā‘il ibn al-Ḥasan ibn Zayd (died 3 October 900), also known as al-Da‘ī al-ṣaghīr ("the Younger Missionary"), was an Alid who succeeded his brother, Hasan ("the Elder Missionary"), as ruler of the Zaydid dynasty of Tabaristan in 884. Little is known of his early life, before coming to Tabaristan after Hasan established Zaydid rule there in 864. He served his brother as a general and governor, and continued his policies after his accession. His reign was troubled by rebellions and wars, most notably by the invasion of Rafi' ibn Harthama in 889–892, which occupied most of his domains. After Rafi' fell out of favour with the Abbasids, Muhammad recovered his position and secured the allegiance of Rafi', but did not particularly support him against the Saffa