Vibhaṅgasutta

Suttapiṭaka · Saṁyuttanikāya · Mahāvaggasaṁyutta · Vol. 19 · Section 928

[928] Bhikkhus, and what is the faculty of joy (somanassindriyaṃ)? Whatever mental pleasure, mental comfort there is, bhikkhus — the pleasant, comfortable feeling (vedanā) born of mind-contact (manosamphassa) — this, bhikkhus, is called the faculty of joy.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 1 other place

Vol. 19 · Section 943 — Tatiyavibhaṅgasutta