Mahasatipatthana Sutta

(Digha Nikaya 22)

Buddha's Discourse over The Great Frames of Reference
Translated from the Pali by Thanissaro Bhikkhu

The Blessed One said this: "This is the direct path for the purification of beings, for the overcoming of sorrow and lamentation, for the disappearance of pain and distress, for the attainment of the right method, and for the realization of Unbinding - in other words, the four frames of reference. What four?
"There is the case where a monk remains focused on the body in and of itself - ardent, alert, and mindful - putting aside greed and distress with reference to the world. He remains focused on feelings...mind...mental qualities in and of themselves - ardent, alert, and mindful - putting aside greed and distress with reference to the world.

Anapanasati Sutta

(Majjhima Nikaya 118)
Buddha discourse on Mindfulness of Breathing

Translated from the Pali by Thanissaro Bhikkhu

"Mindfulness of in-and-out breath, when developed and pursued, is of great fruit, of great benefit. Mindfulness of in-and-out breathing, when developed and pursued, brings the four frames of reference to their culmination. The four frames of reference, when developed and pursued, bring the seven factors of awakening to their culmination. The seven factors of awakening, when developed and pursued, bring clear knowing and release to their culmination.

Sati

excerpt from Mindfulness in Plain English by Venerable Henepola Gunaratana

Mindfulness is the English translation of the Pali word 'Sati.' Sati is an activity. What exactly is that? Well, this is one of those questions without a precise answer, at least not in words. Words are devised by the symbolic levels of the mind and they describe those realities with which symbolic thinking deals. Mindfulness (Sati) is pre-symbolic. It is not shackled to logic. Nevertheless, Mindfulness can be experienced - rather easily - and it can be described, as long as you keep in mind that the words are only fingers pointing at the moon. They are not the thing itself. The actual experience lies beyond the words and above the symbols. Mindfulness could be described in completely different terms than will be used here and each description could still be correct.