From The Sutra of Contemplation of the Dharma Practice of Universal Sage Bodhisattva (Reeves, p410):

Then, with one voice from different mouths, the bodhisattvas will have followers purify their six sense organs.

One will say, “You should reflect on the Buddha.”
Another will say, “You should reflect on the Dharma.”
Another will say, “You should reflect on the monastic community.”
Another will say, “You should reflect on morality.”
Another will say, “You should reflect on generosity.”
Another will say, “You should reflect on the heavens.”

“These six methods express an aspiration to become a buddha. They give birth to bodhisattvas. Before the buddhas, you should now confess your past sins and sincerely repent.