Note 114:2 — PART II. Greek Dualism.
Reading edition
As regards the progress of Buddhism Geiger says:—"We know that in the period after Alexander, Buddhism was powerful in Eastern Iran, and that it counted its confessors as far as Tabaristan. It is especially certain that many Buddhistic priests were found in Bactria. This state of things, which began perhaps in the first century before Christ, lasted till the 7th century A.D., when the appearance of Islamism alone cut short the development of Buddhism in Kabul and Bactria, and it is in that period that we will have to place the rise of the Zarathushtra legend in the form in which it is presented to us by Daqīqī."
Civilisation of Eastern Iranians Vol. II, p. 170.