 The Caliph processed from the Iron Gate towards the Palace of al-Ruṣāfah, and the crowds were lined up as far as al-Muṣalla.Tha'lab remembered clearly the occasion when the caliph raised him up from his father’s arms and said, ‘This is al-Ma’mūn.’ 

Tha'lab was adopted by the military-leader-come-poet Ma’n ibn Zā’idah, of the Banū Shaybān, and became a leading grammarian, philologist traditionist of the Kūfah school.Tha‘lab recalled his interest in Arabic studies, poetry, and language had begun in 831 (216 AH) at age sixteen and that he had memorised to the letter all of al-Farrā’s works, including "Al-Hudūd", by the age of twenty-five.