What EXACTLY did the Buddha say?

The world may never know.  But many scholars thinks he or she know.

Here's an article from an organization that I am not yet familiar with briefly explaining how teachings became text - three months after the Buddha passed away, a First Council happened deciding what should be preserved from his teaching.  The same source talks about how, even though Sanskrit was the language of the educated and priestly caste, Pali is the language of the region at the time when the Buddha lived, his native tongue is said to be closer to a village language called Magadha.

The Pali Cannon is the first collection of the Buddha's teachings, the result of the First Council.