When the Buddha was staying in the town of Sāvatthī, a deity appeared next to him and uttered this verse in his presence:

‍

• Dwelling in the forest,
•      quiescent
•      living the holy life,
• They eat only
•      a single meal
•      each day,
• So why is their countenance
•      so serene?

The Buddha replied:

• They do not
•      lament the past,
• They do not hanker
•      after the future,
• Maintaining themselves
•      in the present,
• Their complexion
•      becomes so serene.
• ‍
• Hankering after
•      the future,
•      lamenting the past,
• Because of this
•      the foolish wither away,
•      Like a fresh reed
• chopped down.

SN 1.10