"Clearly, the Avestan and Vedic names are connected. Since the Vedic name cannot reasonably be said to come from the Avestan, then the Avestan must come from the Vedic. Moreover, the Vedic collocation saptá síndhu- does not occur at all in the very early Books of the RV (i.e. 3, 6, 7) but once only in Bk2 (12.3,12) and Bk4 (28.1), then twice in Bk1 (32.12; 35.8), Bk8 (54.4; 69.12) and Bk10 (43.3; 67.12) and once in Bk9 (66.6). Now in the earliest Maṇḍalas 3,6,7 (as well as later ones) we find collocations like saptá srótas-, srávat-, yahvī- or nadí- but not síndhu-. This then suggests that the Iranians left the Saptasindhu only after the collocation saptá síndhu- had been established by the late Maṇḍalas."