Umm Isa bint Musa al-Hadi

Umm ʿĪsā bint Mūsā al-Hādī (أم عيسى بنت موسى الهادي) was an Abbasid dynasty princess, daughter of caliph al-Hadi, niece of caliph Harun al-Rashid and principal wife of al-Ma'mun, the seventh caliph of the Abbasid Caliphate.

Umm Isa was the daughter of Al-Hadi ((r. 785 – 786)) from one of his concubines. She was born around 783 or 785. She spend her childhood in Baghdad. She was a young child when her father died in 786. Her father was succeeded by her uncle Harun al-Rashid. Her uncle took care of her and her brothers after al-Hadi's death.

Al-Ma'mun married his first wife Umm Isa, the daughter of his uncle al-Hadi, whom he married when he was eighteen years old. They had two sons, Muhammad al-Asghar, and Abd Allah. This marriage was arranged during Harun al-Rashid's reign. Also, The two sons of al-Hadi, Isma'il and Ja'far married Harun-Rashid's daughters, Hamdunah and Fatimah respectively. Thus, the two daughters of Harun were also cousins and sister-in-laws of Umm Isa. She lived a secluded life in the Caliph's harem, only a few things is known about her.

Umm Isa was one or two years older than her husband al-Ma'mun. Her husband was born on the same day when her father died and her uncle ascended to the Caliphate.

Her uncle, caliph Harun al-Rashid had nominated his two elder sons Al-Amin and al-Ma'mun as heir. Already in 792, Harun had Muhammad receive the oath of allegiance (bay'ah) with the name of al-Amin ("The Trustworthy"), effectively marking him out as his main heir, while Abd Allah was not named second heir, under the name al-Maʾmūn ("The Trusted One") until 799. Her husband al-Ma'mun became caliph after the death of her cousin and brother-in-law al-Amin. In 813, al-Amin was beheaded, and al-Maʾmūn became the undisputed Caliph.

Family
Umm Isa was related to the Abbasid ruling House paternally. She was contemporary to several Abbasid caliphs, Abbasid prince and Princesses.