I have heard that on one occasion Ven. Anuruddha was staying near Savatthi in the Dark Forest — diseased, in pain, severely ill. Then a large number of monks went to Ven. Anuruddha and on arrival said to him, "What dwelling1 are you dwelling in so that the pains that have arisen in the body do not invade or remain in the mind?"

"When I dwell with my mind well-established in the four frames of reference, the pains that have arisen in the body do not invade or remain in the mind. Which four? There is the case where I remain focused on the body in & of itself — ardent, alert, & mindful — putting aside greed & distress with reference to the world. I remain focused on feelings in & of themselves... mind in & of itself... mental qualities in & of themselves — ardent, alert, & mindful — putting aside greed & distress with reference to the world. When I dwell with my mind well-established in these four frames of reference, the pains that have arisen in the body do not invade or remain in the mind."