… “And what, bhikkhus, is the path leading to the unconditioned? The four establishments of mindfulness….”
SN43.5: Satipaṭṭhānasutta
Satipaṭṭhānasutta: (5)Establishments of Mindfulness - translated by Bhikkhu Bodhi
Translated by Bhikkhu Bodhi. Source text via SuttaCentral.