Majjhima Nikāya : 37 : Culatanhasankhaya Sutta // The Shorter Discourse on the Destruction of Craving, Pali Canon

When Sakka, king of the gods, spontaneously appeared from beyond and asked The Buddha to describe, in brief, how one is to become enlightened, this was his response :

“Here, ruler of the gods, one has heard that nothing is worth adhering to. When one has heard that nothing is worth adhering to, one directly knows everything; having directly known everything, one fully understands everything; having fully understood everything, whatever feeling one feels, whether pleasant or painful or neither-painful-nor-pleasant, one abides contemplating impermanence in those feelings, contemplating detachment, contemplating cessation, contemplating relinquishment. Contemplating thus one does not cling to anything in the world. When one does not cling, one is not agitated. When one is not agitated, one personally attains Nibbana [enlightenment].

“Briefly, it is in this way, ruler of the gods, that one is liberated in the destruction of craving, one who has reached the ultimate end, the ultimate security from bondage, the ultimate holy life, the ultimate goal, one who is foremost among gods and humans.