Wendy Doniger (1980). Karma and Rebirth in Classical Indian Traditions. [S.l.]: University of California Press. pp. xvii–xviii. ISBN978-0-520-03923-0; Quote: "There was such constant interaction between Vedism and Buddhism in the early period that it is fruitless to attempt to sort out the earlier source of many doctrines, they lived in one another's pockets, like Picasso and Braque (who were, in later years, unable to say which of them had painted certain paintings from their earlier, shared period)."
Bodewitz, Henk (2019). «Chapter 1 – The Hindu Doctrine of Transmigration: Its Origin and Background». In: Heilijgers, Dory H.; Houben, Jan E. M.; van Kooij, Karel. Vedic Cosmology and Ethics: Selected Studies. Col: Gonda Indological Studies. 19. Leiden and Boston: Brill Publishers. pp. 3–19. ISBN978-90-04-40013-9. ISSN1382-3442. doi:10.1163/9789004400139_002
Bodewitz, Henk (2019). «Chapter 1 – The Hindu Doctrine of Transmigration: Its Origin and Background». In: Heilijgers, Dory H.; Houben, Jan E. M.; van Kooij, Karel. Vedic Cosmology and Ethics: Selected Studies. Col: Gonda Indological Studies. 19. Leiden and Boston: Brill Publishers. pp. 3–19. ISBN978-90-04-40013-9. ISSN1382-3442. doi:10.1163/9789004400139_002