Verse 5: Hatred is, indeed, never appeased by hatred in this world. It is appeased only by loving-kindness. This is an ancient law.

1. esa dhammo sanantano: This is the same as “poranako dhammo,” the doctrine followed by the Budhha and his disciples. The exhortation is not to return hatred for hatred but to conquer it by loving-kindness (absence of hatred).

While residing at the Jetavana monastery in Savatthi, the Buddha uttered Verse (5) of this book, with reference to a certain woman who was barren, and her rival.

Once there lived a householder, whose wife was barren; later he took another wife. The feud started when the elder wife caused abortion of the other one, who eventually died in child birth. In later existences the two were reborn as a hen and a cat; a doe and a leopardess; and finally as the daughter of a nobleman in Savatthi and an ogress named Kali. The ogress (Kalayakkhini) was in hot pursuit of the lady with the baby, when the latter learned that the Buddha was nearby, giving a religious discourse at the Jetavana monastery. She fled to him and placed her son at his feet for protection. The ogress was stopped at the door by the guardian spirit of the monastery and was refused admission. She was later called in and both the lady and the ogress were reprimanded by the Buddha. The Buddha told them about their past feuds as rival wives of a common husband, as a cat and a hen, and as a doe and a leopardess. They were made to see that hatred could only cause more hatred, and that it could only cease through friendship, understanding and goodwill.

Then the Buddha spoke in verse as follows:

Verse 5: Hatred is, indeed, never appeased by hatred in this world. It is appeased only by loving-kindness. This is an ancient law.
At the end of the discourse, the ogress was established in Sotapatti Fruition and the long-standing feud came to an end.

Dhammapada Verse 5
Kalayakkhini Vatthu

Na hi verena verani
sammantidha kudacanam
averena ca sammanti
esa dhammo sanantano.

Source: Tipitaka