[308] Bhikkhus, in whomsoever mindfulness directed to the body (kāyagatā sati) has not been developed, not been made much of, Māra gains an opening in him, Māra gains a foothold in him. Bhikkhus, suppose a man were to throw a heavy stone ball onto a heap of wet clay. What do you think, bhikkhus—would that heavy stone ball find an opening into that heap of wet clay?
"It would, venerable sir."
"Even so, bhikkhus, in whomsoever mindfulness directed to the body has not been developed, not been made much of, Māra gains an opening in him, Māra gains a foothold in him."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.