Mohammed esh Sheikh el Mamun, also spelled Muhammad al-Shaykh al-Ma'mun (b. 1566–d. 1613), among other transliterations; also known as Abu Abdallah Mohammed III, ( ) was a member of the Saadian dynasty who ruled parts of present-day Morocco during the succession conflicts within the dynasty between 1603 and 1627. He was the son of Sultan Ahmad al-Mansur by one of his harem slave concubines named Elkheizourân (some cite her name as Eldjauher). He was the full-brother of Abu Faris Abdallah and the half-brother of Zidan Abu Maali.
Muhammad al-Shaykh al-Ma'mun had been designated by his father, Ahmad al-Mansur, in 1579 and again in 1584 to be his successor. He was, however, also imprisoned by his father at some point for rebellion. It was during the reign of Muhammad al-Shaykh al-Ma'mun that the division of the Saadian realm arose: one part ruled from the main capital in Marrakesh, and the other from Fez in the north.
Control of both regions changed hands multiple times. In 1604, Muhammad al-Shaykh al-Ma'mun defeated his brother Zidan Abu Maali who was ruling from Fez, However, his concession of Larache to the Spanish quickly eroded his political support and also weakened the larger Saadian dynasty's prestige, resulting in local religious leaders and marabouts increasingly challenging Saadian rule.