Al-Mahdī’s mother—may Allah have mercy upon her—was Umm Mūsā, daughter of Manṣūr ibn ʿAbd Allāh al-Ḥimyarī.

Al-Mahdī related through his father, through his grandfather, through his forefather ʿAbd Allāh ibn ʿAbbās, that the Messenger of Allah ﷺ recited aloud the basmala—“Bismi-llāh al-Raḥmān al-Raḥīm.” Yḥyā ibn Ḥamzah al-Batalhiyy (1), the judge of Damascus, transmitted this report from him and stated that he once prayed behind al-Mahdī when the caliph arrived in Damascus; during the prayer al-Mahdī recited the basmala aloud in both surahs and traced the practice back to the Messenger of Allah ﷺ. More than one transmitter narrated the report from Yḥyā ibn Ḥamzah. Al-Mahdī also transmitted it from al-Mubārak ibn Faḍālah; and it was further narrated from him by Jaʿfar ibn Sulaymān al-Ḍubāʿī, Muḥammad ibn ʿAbd Allāh al-Raqāshī, and Abū Sufyān Saʿīd ibn Yḥyā ibn al-Mahdī (2).

Al-Mahdī was born either in 126 or 127 AH, or—as another opinion has it—in 121 AH. He assumed the caliphate in Dhū al-Ḥijjah 158 AH after the death of his father, being then thirty-three years of age. His birthplace was al-Ḥumaymah in the district of al-Balqāʾ. He passed away in Muḥarram of the present year, 169 AH, at the age of either forty-three or forty-eight. His reign lasted ten years, one month, and some additional days. He was dark-complexioned, tall, and curly-haired; on one of his eyes there was a small white spot—some said on the right eye, others on the left.

Al-Rabīʿ the chamberlain recounted: “I once saw al-Mahdī praying on a moon-lit night in one of his porticos. He wore splendid garments, and I could not tell which was more beautiful—he, the moon, the portico, or his clothes. He recited, ‘But should you turn away, will you not perhaps spread corruption in the land and sever your ties of kinship?’ (Q 47:22). Then he ordered me to bring one of his imprisoned kinsmen, and he set him free.”

When news of his father’s death reached him in Mecca, as mentioned earlier, he concealed the matter for two days. On Thursday a public crier announced, “The prayer is assembling!” Al-Mahdī rose to address the people and informed them of his father’s passing, saying, “The Commander of the Believers was summoned and has answered. I count the Commander of the Believers with Allah, and I seek His help in shouldering the caliphate of the Muslims.” The people thereupon pledged allegiance to him that very day.

Abū Dulāmah offered him both condolences and congratulations in a poem that opens:
One eye of mine is plainly seen exultant—
delighting in its ruler—while the other sheds tears.
It weeps and laughs by turns: distressed
by what it disavows, gladdened by what it knows.