Vibhaṅgasutta

Suttapiṭaka · Saṁyuttanikāya · Mahāvaggasaṁyutta · Vol. 19 · Section 860

[860] And what, bhikkhus, is the faculty (indriya) of energy (vīriya)? Here, bhikkhus, a noble disciple dwells with energy aroused for the abandoning of unwholesome dhammas and for the acquisition of wholesome dhammas; he is strong, firm in exertion, not shirking the responsibility of cultivating wholesome dhammas. This, bhikkhus, is called the faculty of energy.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 1 other place

Vol. 19 · Section 872 — Mudutavagga