At Sāvatthī.

Now at that time Venerable Mahākappina was sitting not far from the Buddha, cross-legged, his body set straight, and mindfulness established in his presence. The Buddha saw him, and addressed the mendicants:

“Mendicants, do you see any disturbance or trembling in that mendicant’s body?”

“Sir, whenever we see that mendicant meditating—whether in the middle of the Saṅgha or alone in private—we never see any disturbance or trembling in his body.”

“Mendicants, when an immersion has been developed and cultivated there’s no disturbance or trembling of the body or mind. That mendicant gets such immersion when he wants, without trouble or difficulty. And what is that immersion?

When immersion due to mindfulness of breathing has been developed and cultivated there’s no disturbance or trembling of the body or mind. And how is immersion due to mindfulness of breathing developed and cultivated in such a way?

It’s when a mendicant—gone to a wilderness, or to the root of a tree, or to an empty hut—sits down cross-legged, sets their body straight, and establishes mindfulness in their presence. Just mindful, they breathe in. Mindful, they breathe out. … They practice like this: ‘I’ll breathe in observing letting go.’ They practice like this: ‘I’ll breathe out observing letting go.’

That’s how immersion due to mindfulness of breathing is developed and cultivated so that there’s no disturbance or trembling of the body or mind.”