Harun had made Yahya his vizier when…
787 CE
Harun had made Yahya his vizier when he became caliph.
Under Yahya's influence, the Caliph invites to Baghdad many scholars and masters from India, especially Buddhists.
A catalogue of both Muslim and non-Muslim texts prepared at this time, Kitab al-Fihrist, includes a list of Buddhist works.
Among them is an Arabic version of the account of Buddha’s previous lives, Kitab al-Budd.