At Sāvatthi.

"Whether in the past, present, or future, bhikkhus, all those arahants and perfectly enlightened ones have truly understood the four noble truths as they really are. And what are these four? The Noble Truth of suffering, the Noble Truth of the arising of suffering, the Noble Truth of the ending of suffering, the Noble Truth of the way of practice leading to the ending of suffering. Just as those in the past have fully understood these truths, so will those in the future, and so do those in the present.

Therefore, bhikkhus, effort should be made to fully understand: 'This is suffering'; effort should be made to fully understand: 'This is the arising of suffering'; effort should be made to fully understand: 'This is the ending of suffering'; effort should be made to fully understand: 'This is the way of practice leading to the ending of suffering.'"