Samyutta Nikaya
The Four Noble Truths are the most fundamental Buddhist teachings and appear countless times throughout the most ancient Buddhist texts, the Pali Canon. They arose from Buddha's enlightenment and are regarded in Buddhism as deep spiritual insight, "not as philosophical theory", with Buddha noting in the Samyutta Nikaya: "These Four Noble Truths, monks, are actual, unerring, not otherwise. Therefore, they are called noble truths."