There is a treaty signed by the Mitanni kingdom which invokes deities found in the Rig Veda.

https://www.jstor.org/stable/595878?seq=1

Indra, Varuna, Mitra and the Nasatyas (Ashvins) occur in a Mitanni trearty as witnesses and there is a Rig Vedic verse in which they occur in the same order.

The Indus Valley artifacts and script also suggest very early Hinduism.

Is Indus Valley Civilization off-topic at HSE?

shows evidence that IVC could be called Hindu.