Ummādantījātaka

Suttapiṭaka · Khuddakanikāya · Jātaka (2) · Vol. 28 · Section 35

[35] Whoever measures the suffering (dukkha) of another by his own suffering, or his own happiness by [another's] happiness, [knowing,] "Just as this is for me, so it is for others" — whoever understands thus has known the Dhamma.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.