In the beginning, the original Supreme Personality manifested the form of Brahmā through the material mode of passion in order to create this universe. The Lord manifested His form as Viṣṇu, the Lord of sacrifice and protector of the twice-born brāhmaṇas and their religious duties, to maintain the universe. And when the universe is to be annihilated the same Supreme Lord employs the material mode of ignorance and manifests the form of Rudra. The created living beings are thus always subject to the forces of creation, maintenance and destruction.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
आदावभूच्छतधृती रजसास्य सर्गे विष्णुः स्थितौ क्रतुपतिर्द्विजधर्मसेतुः । रुद्रोऽप्ययाय तमसा पुरुषः स आद्य इत्युद्भवस्थितिलयाः सततं प्रजासु
ādāvabhūcchatadhṛtī rajasāsya sarge viṣṇuḥ sthitau kratupatirdvijadharmasetuḥ | rudro'pyayāya tamasā puruṣaḥ sa ādya ityudbhavasthitilayāḥ satataṃ prajāsu
SB 11.4.5