“Yes — the one who waged war his whole life long and conquered the entire earth, and then renounced his kingdom in order to rest.”
Arjuna, do you know of Emperor Muchukunda, the son of Emperor Mandhata? Yes — the one who waged war his whole life long and conquered the entire earth, and then renounced his kingdom in order to rest. Arjuna, wondrous is the one who comes to know that the world is toil, and that austerity (tapasya) is the only rest.
Arjuna, do you know of Emperor Muchukunda, the son of Emperor Mandhata?
Chapter 20 of 35 — a single teaching, 1 min in total.
The story belongs to the Krishna cycle rather than to the Mahabharat's war narrative — it is told in the Harivamsa and the Puranas. Muchukunda, a king who had fought for the gods until he was exhausted, asks for sleep as his reward, with the condition that whoever wakes him is burnt to ash. Krishna later leads a pursuing enemy into that cave, and lets the boon do the rest.
It is usually read as a story about a favour granted exactly as asked. Rest, in it, is not idleness but the thing a person may legitimately want after enough has been asked of them — and it is defended fiercely.