One verse

Srimad Bhagavatam 9.24.56

9.24.56

यदा यदा हि धर्मस्य क्षयो वृद्धिश्च पाप्मन: । तदा तु भगवानीश आत्मानं सृजते हरि: ॥ ५६ ॥

yada yada hi dharmasya ksayo vrddhis ca papmanah tada tu bhagavan isa atmanam srjate harih

yada
whenever
yada
when ever
hi
indeed
dharmasya
of the principles of religion
ksayah
deterioration
vrddhih
increasing
ca
and
papmanah
of sinful activities
tada
at that time
tu
indeed
bhagavan
the Supreme Personality of Godhead
isah
the supreme controller
atmanam
personally
srjate
descends
harih
the Supreme Personality of Godhead.

Whenever the principles of religion deteriorate and the principles of irreligion increase, the supreme controller, the Personality of Godhead Sri Hari, appears by His own will.