Dhammapada · 22.10

Nagaraṃ yathā paccantaṃ, guttaṃ santarabāhiraṃ;Evaṃ gopetha attānaṃ, khaṇo vo mā upaccagā;Khaṇātītā hi socanti, nirayamhi samappitā.

Nagaram yatha paccantam, guttam santarabahiram; Evam gopetha attanam, khano vo ma upaccaga; Khanatita hi socanti, nirayamhi samappita.

Like a frontier city guarded within and without, so guard yourself. Let the moment not pass you by — those who let the moment pass grieve, consigned to hell.

— Dhammapada 22.10

Source: Pali text from the Khuddaka Nikāya of the Pali Canon (oldest extant Buddhist scripture, compiled c. 3rd century BCE). Public-domain English readings drawn from F. Max Müller's translation in Sacred Books of the East, Vol X (1881) and the Buddhist Publication Society's freely-licensed Acharya Buddharakkhita rendering.