"H. Kern in his book Over het woord Zarathushtra (1867) states, “the Bactrian (i.e. Avestan) is so (greatly) related to the Old- Indian language (Vedic), and in particular, that of the Vedas, that without exaggeration it can be called a dialect thereof.”"
January 1, 1970
https://en.wikiquote.org/wiki/Johan_Hendrik_Caspar_Kern