One verse

Srimad Bhagavatam 7.12.23

7.12.23

यदाकल्प: स्वक्रियायां व्याधिभिर्जरयाथवा । आन्वीक्षिक्यां वा विद्यायां कुर्यादनशनादिकम् ॥ २३ ॥

yadakalpah sva-kriyayam vyadhibhir jarayathava anviksikyam va vidyayam kuryad anasanadikam

yada
when
akalpah
unable to act
sva-kriyayam
in one’s own prescribed duties
vyadhibhih
because of disease
jaraya
or because of old age
athava
either
anviksikyam
in spiritual advancement
va
or
vidyayam
in the advancement of knowledge
kuryat
one must do
anasana-adikam
not take sufficient food.

When because of disease or old age one is unable to perform his prescribed duties for advancement in spiritual consciousness or study of the Vedas, he should practice fasting, not taking any food.