[134] Then the Venerable Rāhula thought: "Who, today, having been exhorted by the Blessed One with an exhortation face to face, would enter the village for alms?" Turning back from there, he sat down at the root of a certain tree, having folded his legs crosswise, set his body erect, and established mindfulness (sati) before him. The Venerable Sāriputta saw the Venerable Rāhula sitting at the root of a certain tree, having folded his legs crosswise, set his body erect, and established mindfulness before him; and having seen him, he addressed the Venerable Rāhula: "Rāhula, develop the meditation of mindfulness of breathing (ānāpānasati). Mindfulness of breathing, Rāhula, when developed and cultivated, is of great fruit and great benefit."
Then, in the evening, the Venerable Rāhula, having emerged from seclusion, approached the Blessed One; having approached and paid homage to the Blessed One, he sat down to one side. Seated to one side, the Venerable Rāhula said to the Blessed One: "Venerable sir, how is mindfulness of breathing developed, how is it cultivated, so that it is of great fruit and great benefit?"
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.