MN 10 The Foundations of Mindfulness - Satipaṭṭhāna Sutta
This is the most important discourse by the Buddha on the training of
mindfulness meditation, with particular attention given to developing
insight. The Buddha begins by declaring that the four foundations of
mindfulness are the direct path leading to the realization of Nibbāna.
He then gives detailed instructions on the four foundations: the
contemplation of the body, feelings, mind, and mind objects.