All Buddhas Become Awakened Through the Four Noble Truths

At Savatthi.

“Bhikkhus, whatever Arahants, Perfectly Enlightened Ones, in the past fully awakened to things as they really are, all fully awakened to the Four Noble Truths as they really are. Whatever Arahants, Perfectly Enlightened Ones, in the future will fully awaken to things as they really are, all will fully awaken to the Four Noble Truths as they really are. Whatever Arahants, Perfectly Enlightened Ones, at present have fully awakened to things as they really are, all have fully awakened to the Four Noble Truths as they really are.

“What four?

The noble truth of suffering, the noble truth of the origin of suffering, the noble truth of the cessation of suffering, the noble truth of the way leading to the cessation of suffering. Whatever Arahants, Perfectly Enlightened Ones, fully awakened … will fully awaken … have fully awakened to things as they really are, all have fully awakened to these Four Noble Truths as they really are.

“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.’”

Arahantasutta SN 56.24 https://suttacentral.net/sn56.24