The Virtuous One Sutta - Buddhism - translated by Suddhāso Bhikkhu

Mahākoṭṭhita asks what an ethical mendicant should focus on, and Sāriputta replies that if they focus on aggregates as impermanent, etc. they may become a stream-enterer. A stream-enterer contemplating in the same way may become a non-returner, a once-returner, and a perfected one.