Four Noble Truths
The Four Noble Truths are heart of the Buddhism and contain an incontrovertible fact.
In the Rohitassa Sutta the Buddha states:
"In this very one-fathom long body along with its perceptions and thoughts, do I proclaim suffering, the origin of suffering, the cessation of suffering, and the path leading to the cessation of suffering."
- Samyutta Nikāya
"Light arose in me in things not heard before."
- the Lord Buddha, Dhammacakka Sutta