Yet the earliest surviving (extant) manuscript of any of Siddhartha Gautama (who lived in South Asia during the 6th or maybe 5th century BC) teachings date from the first century BC to the third century AD, found in Afghanistan - hundreds of years after his existence - and there is no single textual collection for all of Buddhism, being were not committed to writing until some centuries after the death of Gautama Buddha. cf. https://en.wikipedia.org/wiki/Buddhist_texts
Not a good climate for document preservation, and Buddhism declined in its Indian homeland.
https://search.brave.com/search?q=oldest+surviving+text+of+old+testament
https://search.brave.com/search?q=oldest+surviving+text+of+new+testament