"Monks, there are these four establishings of mindfulness. Which four?
"There is the case where a monk remains focused on the body in & of itself — ardent, alert, & mindful — subduing greed & distress with reference to the world. For him, remaining focused on the body in and of itself, the body is comprehended. From the comprehension of the body, the deathless is realized.
"He remains focused on feelings in & of themselves — ardent, alert, & mindful — subduing greed & distress with reference to the world. For him, remaining focused on feelings in & of themselves, feelings are comprehended. From the comprehension of feelings, the deathless is realized.
"He remains focused on the mind in & of itself — ardent, alert, & mindful — subduing greed & distress with reference to the world. For him, remaining focused on the mind in and of itself, the mind is comprehended. From the comprehension of the mind, the deathless is realized.
"He remains focused on mental qualities in & of themselves — ardent, alert, & mindful — subduing greed & distress with reference to the world. For him, remaining focused on mental qualities in & of themselves, mental qualities are comprehended. From the comprehension of mental qualities, the deathless is realized."
See also: SN 22.23.