"Night of the three Caliphs": Harun al-Rashid becomes the Abbasid caliph upon the death of his brother al-Hadi. Birth of Harun's son al-Ma'mun.

Abū Jaʿfar Hārūn ibn Muḥammad ar-Rāshīd, or simply Hārūn ibn al-Mahdī, famously known as Hārūn al-Rāshīd, was the fifth Abbasid caliph of the Abbasid Caliphate, reigning from September 786 until his death in March 809. His reign is traditionally regarded to be the beginning of the Islamic Golden Age. His epithet al-Rashid translates to "the Just", "the Upright", or "the Rightly-Guided".

Abū Muḥammad Mūsā ibn al-Mahdī al-Hādī better known by his laqab al-Hādī (الهادي‎) was the fourth Arab Abbasid caliph who succeeded his father al-Mahdi and ruled from 169 AH until his death in 170 AH. His short reign ended with internal chaos and power struggles with his mother.

Abū al-ʿAbbās Abd Allāh ibn Hārūn al-Maʾmūn, better known by his regnal name al-Ma'mun, was the seventh Abbasid caliph, who reigned from 813 until his death in 833. His leadership was marked by the power and prosperity of the Abbasid Caliphate, al-Ma'mun promoted the Graeco-Arabic translation movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra". Making him one of the most important caliphs in the Islamic Golden Age. He is also known as a proponent of the rational Islamic theology of Mu'tazilism.

September 14 is the 257th day of the year in the Gregorian calendar; 108 days remain until the end of the year.