Dhamma Verses (Dhammapada, KN 2)

22: The Chapter about the Underworld – 272
Watch over oneself carefully
Some monks spent the Rains Retreat in the border country, but
after some time the village was attacked and the inhabitants
had to spend all their time reinforcing the village, and did not
look after the monks well; later they reported the matter to the
Buddha, who taught them with this verse.
315. Nagaraṁ yathā paccantaṁ guttaṁ santarabāhiraṁ,
evaṁ gopetha attānaṁ, khaṇo vo mā upaccagā,
khaṇātītā hi socanti nirayamhi samappitā.
As a border town is guarded
on the inside and the outside,
so one should watch over oneself,
and should not let the moment pass,
for when the chance has passed they grieve,
when consigned to the underworld.