The Buddha and Rāhula are on their way to the village for alms, and the Buddha tells Rāhula that all rūpa should be regarded as anattā, and not only rūpa, but also the other khandhas. Rāhula stops and sits under a tree meditating. Sāriputta approaches and suggests that he should develop ānāpānasati. Later in the evening Rāhula asks the Buddha how he can do this. The Buddha describes how it is done by regarding all the elements earth, water, fire, air and space, both personal and external with disgust and loathing of heart. One should not allow sensory impressions to lay hold of one's heart, just as the earth remains impassive whatever may be thrown upon it. It is so with the other elements. One should grow in loving-kindness, compassion, in gladness over the welfare of others, in equanimity, contemplation of the body's corruption, perception of the fleeting nature of things, and in the mindfulness which comes from ordered breathing.
M.i.420 6; it is perhaps a part of this sutta which is quoted at Mil. 385, 388; see Mil. Trs.ii.312, n.1.