One verse

Srimad Bhagavatam 7.14.37

7.14.37

पुराण्यनेन सृष्टानि नृतिर्यगृषिदेवता: । शेते जीवेन रूपेण पुरेषु पुरुषो ह्यसौ ॥ ३७ ॥

purany anena srstani nr-tiryag-rsi-devatah sete jivena rupena puresu puruso hy asau

purani
residential places or bodies
anena
by Him (the Supreme Personality of Godhead)
srstani
among those creations
nr
man
tiryak
other than human beings (animals, birds, etc)
rsi
saintly persons
devatah
and demigods
sete
lies down
jivena
with the living entities
rupena
in the form of Paramatma
puresu
within these residential places or bodies
purusah
the Supreme Lord
hi
indeed
asau
He (the Personality of Godhead)

The Supreme Personality of Godhead has created many residential places like the bodies of human beings, animals, birds, saints and demigods. In all of these innumerable bodily forms, the Lord resides with the living being as Paramatma. Thus He is known as the purusavatara.