Saṃyutta Nikāya 56
Connected Discourses on the Truths
23. The Perfectly Enlightened One
At Savatthi. “Bhikkhus, there are these Four Noble Truths. What four? The noble truth of suffering … the noble truth of the way leading to the cessation of suffering. It is because he has fully awakened to these Four Noble Truths as they really are that the Tathagata is called the Arahant, the Perfectly Enlightened One.
“Therefore, bhikkhus, an exertion should be made to understand: ‘This is suffering.’… An exertion should be made to understand: ‘This is the way leading to the cessation of suffering.’”