Chappāṇakopamasutta

sn35.247:6.1 ‘A strong post or pillar’ is a term for mindfulness of the body.

sn35.247:6.2 So you should train like this:

sn35.247:6.3 ‘We will develop mindfulness of the body. We’ll cultivate it, make it our vehicle and our basis, keep it up, consolidate it, and properly implement it.’

sn35.247:6.4 That’s how you should train.”