After the onset of Islam to the Aryan kingdom (Ērānšahr), the death of Yazdegird caused the learned tradition of the first teachers to be broken, for the second time. The priestly schools were closed, and the text corpus of the religion was reduced in volume. The Muslim conquest of India – nearly four centuries after that of Persia –, just as Bērōnī has related, was to be less crushing than that of Persia, and yet he said:
“Maḥmūd utterly ruined the prosperity of the country, and performed there wonderful exploits, by which [the Indo-Aryans] became like atoms of dust scattered in all directions, and like a tale of old in the mouth of the people. Their scattered remains cherish, of course, the most inveterate aversion towards all Muslims. This is the reason, too, why [the Indian] sciences have retired far away from those parts of the country conquered by us, and have fled to places which our hand cannot get reach.” (Bērōnī’s India تحقيق ماللهند in 11/22)
The Muslims were not able to subject the whole India; while, although some Perso-Aryan princes tried to assume royal power in the eastern parts of the Aryan land, but the attack of Qutaiba b. Muslim (between A.D. 705 and 715) to Sogdiana and Chorasmia put an end to this hope – there was no place in Persia which their hand could not reach. In the days of the same Maḥmūd, as Nizām al-Mulk has said, “No Mazdayasnian (gabr) … would dare appear in an open ground [in Persia] nor even go in the presence of a Turk.”
Bērōnī who was from Chorasmia, the land on the lower course of the Oxus, has described the onset of Islam to his land (A.D. 712) thus :
« Qutaiba b. Muslim had extinguished those who knew elegantly the Chorasmian writing (that is, the scribes), who knew the history of the country, and who taught their sciences to others, and he scattered the whole (culture of ancient Chorasmia, including the neglect of irrigation works and the decline of urban life). In consequence, these things are involved in so much obscurity, that it is impossible to obtain an accurate knowledge of the ancient history of the country before the time of Islam.” (The Vestiges of the Past, 3.51)
Again:
“Once Qutaiba b. Muslim of Bāhil [conquered Chorasmia], he caused to perish the scribes (کاتب ), killed the scholar-priests (هربذ ), and burnt their books and papers.” (Ibid. 5.16.)
The Royal Library transferred by the last Persian king Yazdegird to his last refuge, Marv, fell into the hands of the Muslims. Aḥmad b. Abi Ṭāhir (about 819-893), a man of Persian origin, says that: ‘Attābī, a secretary and poet from Syria (who died 835) related that he had consulted thrice Persian (Pārsīg) books in that library in ruin.
Soon after his visits, not only the library of Marv disappeared, but also nobody would dare hold any Pārsīg manuscript. Daulatšāh says that one day, in Nēšābuhr, some Persian man offered a copy of the Persian romance of Vāmiq u ‘Aδrā to ‘Abd-Allāh b. Ṭāhir (who ruled in central and eastern Persia during 830-45). The Muslim ruler ordered this copy to be destroyed, and all other Persian and Mazdayasnian (Magian) books in his territories to be burnt. (۳۰ ، دولتشاه سمرقندی، تذکره، بريل، ۱۹۰۰)
The Perso-Aryans, lacked royal power, threatened with extinction, were faced to migrate: Some left Persia, settled in Gujarat, founding the Parsi Community in India; some others sought refuge in the remote oases of Yazd and Kirmān. In this way, they preserved in part the sacred literature of the ancients.