A deity asks the Buddha how the complexion of those dwelling in the wilderness and living the holy life becomes serene.

At Sāvatthi.

While standing to one side, that deity addressed the Blessed One with a verse:

“For those dwelling in the wilderness, peaceful ones who live the holy life; Eating only one meal a day, how does their complexion become serene?”

[The Blessed One]: "They don’t grieve over the past, nor do they yearn for the future; They continue to live through the present, by this, their complexion becomes serene.

By yearning for the future, and by grieving over the past; Ignorant persons dry up and wither away, like a green reed cut down."

Related Teachings:

Ailing in body and healthy in mind (SN 22.1) ↗️ - The householder Nakulapitā asks the Buddha for help in coping with old age. The Buddha says to reflect: “Even though I am afflicted in body, my mind will be unafflicted.” Later Sāriputta explains this in terms of the five aggregates.

Mindfulness of body (AN 1.591 - 1.615) - In these series of short teachings, the Buddha is sharing on maintaining a recollection to be aware as one is interacting with the world. One can gradually practice in training in this way by picking one activity and aiming to maintain awareness during this activity.

A regular practice of meditation clears the mind of obstructions - A steady practice of meditating 2x to 3x per day leads to cultivation of mindfulness of the present phenomena.