al-Hadi (Musa)

Musa al-Hadi ibn Muhammad al-Mahdi ibn Abi Ja'far al-Mansur, the fourth Abbasid caliph; his mother was al-Khayzuran. He was born at al-Rayy in 147 AH, was acclaimed caliph after his father in 169 AH, reigned a year and some months, and died in Rabi' al-Akhar 170 AH ^{1 2}.

Al-Mahdi had him acclaimed as heir in 159 AH, followed by Harun al-Rashid; when al-Mahdi died in 169 AH al-Hadi was acclaimed under his father's designation, and al-Khatib notes that no one had held the caliphate at his age before ^{1 2}. Al-Suyuti reports that his father charged him with pursuing the zanadiqa, which he did energetically, and that he was the first to have men walk before him with drawn swords, lances and strung bows, a pomp his officials imitated so that arms multiplied in his time ².

He died in Rabi' al-Akhar 170 AH, and accounts of the cause differ: a fall from a bank with a drinking companion in which a reed stalk entered him; an internal abscess; or poisoning by his mother al-Khayzuran when he resolved to advance his son over his brother al-Rashid ³. He left seven sons ⁴.

• The causes of death conflict within al-Suyuti's own account and are given here as transmitted, without adjudication.