SN 1.10
PTS: S i 4
CDB i 93
Arañña Sutta: The Wilderness
translated from the Pali by
Thanissaro Bhikkhu
Alternate translations: Ireland | Olendzki

Standing to one side, a devata addressed the Blessed One with a verse:

Living in the wilderness, staying peaceful, remaining chaste, eating just one meal a day: why are their faces so bright & serene?

[The Buddha:]

They don't sorrow over the past, don't long for the future. They survive on the present. That's why their faces are bright & serene. From longing for the future , from sorrowing over the past, fools wither away like a green reed cut down.