Satisutta

Suttapiṭaka · Saṁyuttanikāya · Mahāvaggasaṁyutta · Vol. 19 · Section 682

[682] On one occasion the Blessed One was dwelling at Vesālī, in Ambapāli's Grove. There the Blessed One addressed the bhikkhus: "Bhikkhus!" "Venerable sir," those bhikkhus replied to the Blessed One. The Blessed One said this: "Bhikkhus, a bhikkhu should dwell mindful (sati) and clearly comprehending (sampajāno). This is our instruction (anusāsanī) to you."

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 1 other place

Vol. 18 · Section 382 — Dutiyagelaññasutta