 Some of the Twelver sect of Shia Muslims blame Harun for his supposed role in the murder of their 7th Imam (Musa ibn Ja'far).Hārūn was born in Rey, then part of Jibal in the Abbasid Caliphate, in present-day Tehran Province, Iran.He was the son of al-Mahdi, the third Abbasid caliph (ruled 775 – 786), and al-Khayzuran, a former slave girl from Yemen, who was a woman of strong personality and who greatly influenced affairs of state in the reigns of her husband, mother and sons.