Asaṅkiya Jātaka (No.76)
The Bodhisatta was born as a brahmin in Bārāṇasī and became an ascetic. In the course of his wanderings he once travelled with a merchant caravan. The caravan halted for the night, but while the merchants slept, the ascetic spent his time pacing up and down. Robbers, coming to plunder the caravan, were prevented from so doing by the watchfulness of the ascetic. The next day the merchants, discovering what had happened, asked him if he had felt no fear at the sight of the robbers. “The sight of robbers causes what is known as fear only to the rich. I am penniless, why should I be afraid?” he answered.
After death he was born in the Brahma world.
The story was told to a lay disciple of Sāvatthi who had likewise prevented a caravan from being robbed. “In guarding himself a man guards others; in guarding others he guards himself.” J.i.332‑4.