B.G 10.21
Among the Ādityas, I am Viṣṇu; among luminous bodies, I am the radiant Sun; among the Maruts, I am Marīci; among the stars, I am the Moon.
Gīta Bhāshya 10.21
He is called 'Viṣṇu' because he is the: mover of all beings and creatures, pervades the heavens and the earth, supreme splendor, dwells in the beings, their intentionality, and traverser. Root 'viṣlṛ' means to pervade, and 'viśa' means to enter.
He is called 'Viṣṇu' because of his all-pervading and penetrative nature.
"'viṣlṛ' means to pervade, and 'viśa' means to enter."
- thus is the recitation.
"O Bhārata, I am the mover of all beings and creatures; I pervade the heavens and the earth; my splendor is supreme; I dwell in the beings and am their intentionality too; and I traverse - O Pārtha, Hence I am known as Viṣṇu."
- stated thus in the Mokṣa-dharma section (of the Mahābhārata).