Yudhishthira calls Dharma the best friend in the Yaksha Prashna episode of the Mahabharata. This is revealed through a series of questions posed by a Yaksha (a forest spirit) to Yudhishthira, and his subsequent answers.

When asked who a man's best friend is, Yudhishthira replies:

His reasoning is that Dharma accompanies a person even after death. Wealth and relationships are temporary and left behind in the mortal world, but the consequences of one's righteous actions (Dharma) follow the soul into the afterlife, shaping their future existence.

Essentially, Yudhishthira emphasizes the importance of living a virtuous and righteous life, as these actions provide enduring benefits beyond death.