[319] And how, bhikkhus, is a bhikkhu devoted to wakefulness? Here, bhikkhus, during the day a bhikkhu purifies his mind (citta) of obstructive states by walking and by sitting. In the first watch of the night he purifies his mind of obstructive states by walking and by sitting. In the middle watch of the night he lies down on his right side in the lion's posture, placing one foot upon the other, with mindfulness and clear comprehension, having attended to the perception of rising. In the last watch of the night, having risen, he purifies his mind of obstructive states by walking and by sitting. It is in this way, bhikkhus, that a bhikkhu is devoted to wakefulness.
Bhikkhus, endowed with these three qualities, a bhikkhu dwells with abundant happiness and gladness in this very life, and the groundwork has been laid by him for the destruction of the taints (āsava).
The second [sutta].
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.