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
The Four Noble Truths which the Buddha Himself discovered by His own intuitive knowledge. Whether the Buddhas arise or not these Truths exist, and it is a Buddha that reveals them to the deluded world. They do not and cannot change with time because they are eternal Truths. The Buddha was not indebted to anyone for his realization of them. He himself said: "They were unheard before."
"Light arose in me in things not heard before."
- the Lord Buddha, Dhammacakka Sutta