Historically North India had a religion based on the Vedas and led by Brahmin priests. Scholars argue over whether this ancient religion was Hinduism or not. It is called by various names, Brahmanism, Vedism, Vedic Brahmanism, ancient Hinduism, etc.
The next period in the history of Indian religion is the Reform period or Shramanic period. This is where many people chose to forgo the rites and rituals of the Vedic period and become wandering mendicants (sramanas) in search of answers to questions like, “How can I find union with God?” and “Why is there suffering?”. This period gave rise to texts like the Upanishads and sramanas like Mahavira who founded Jainism and Gautama Siddhartha, who would become the Buddha.
During this time, Gautama Siddhartha studied with two different teachers, Arada Kalama (Alara Kalama in Pali) and Udraka Ramaputra (Udaka Ramaputta in Pali). Under Arada, he learned an early form of Samkhya, which would become one of the six schools of classical and modern Hinduism. He also learned shamatha meditation and how to enter a dhyana called the sphere of nothingness.
Gautama became the equal of Arada, so Arada invited him to be an equal partner leading his sangha. Gautama did not find that the sphere of nothingness ended suffering, declined the offer and went to study with Udaka Ramaputta.
Udaka taught an early form of yoga, which would also become one of the six schools of classical and modern Hinduism. He learned how to enter the immaterial attainments. Once he could attain and sustain this state at will, he realized that this could not help him with his quest, so he struck out on his own.
The next period of Indian religion that occurred about 200 years after the death of the Buddha is called Classical Hinduism. This started with the “Hindu synthesis” which took Vedic Brahmanism, the six schools (Yoga, Vedanta, Samkhya, Mimamsa, Nyaya and Vaisheshika) and combined them with aspects of Buddhism and Jainism.
Gautama rejected the version of the Vedas extant during his life as having been corrupted. He rejected rites and rituals and the cast system, so he had no need for Brahmin priest. For these reasons, he wasn’t a practitioner of Vedic Brahmanism.
Although some scholars would say that Hinduism had yet been developed, Gautama before becoming a Buddha was clearly a sramana and practiced both Samkhya and Yoga. For this reason, I think you could safely call him a Hindu at this point.
©2017 Stephen L. Martin
Photo: Statue of the Buddha from when he tried asceticism as a path to find the answers he was looking for.