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 dwelling[1] 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."