Appamaññāvibhaṅgasuttantabhājanīya

Abhidhammapiṭaka · Vibhaṅga · Vol. 35 · Section 746

[746] And how does a bhikkhu dwell pervading one direction with a mind accompanied by altruistic joy (muditā)? Just as, on seeing one person who is dear and agreeable, he would be gladdened, even so he pervades all beings with altruistic joy.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.