At Sāketa. Sāriputta said to Anuruddha:

“Reverend Anuruddha, what things should a mendicant who is an adept enter and remain in?”

“Reverend Sāriputta, a mendicant who is an adept should enter and remain in the four kinds of mindfulness meditation. What four? It’s when a mendicant meditates by observing an aspect of the body—keen, aware, and mindful, rid of desire and aversion for the world. They meditate observing an aspect of feelings … mind … principles—keen, aware, and mindful, rid of desire and aversion for the world. A mendicant who is an adept should enter and remain in these four kinds of mindfulness meditation.”