Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 15


तल्लोकपद्मं स उ एव विष्णु:प्रावीविशत्सर्वगुणावभासम् ।तस्मिन् स्वयं वेदमयो विधातास्वयम्भुवं यं स्म वदन्ति सोऽभूत् ॥ १५ ॥


tal loka-padmaṁ sa u eva viṣṇuḥprāvīviśat sarva-guṇāvabhāsamtasmin svayaṁ vedamayo vidhātāsvayambhuvaṁ yaṁ sma vadanti so ’bhūt


Into that universal lotus flower Lord Viṣṇu personally entered as the Supersoul, and when it was thus impregnated with all the modes of material nature, the personality of Vedic wisdom, whom we call the self-born, was generated.


This lotus flower is the universal virāṭ form, or the gigantic form of the Lord in the material world. It becomes amalgamated in the Personality of Godhead Viṣṇu, in His abdomen, at the time of dissolution, and it becomes manifest at the time of creation. This is due to Garbhodakaśāyī Viṣṇu, who enters into each of the universes. In this form is the sum total of all the fruitive activities of the living entities conditioned by material nature, and the first of them, namely Brahmā, or the controller of the universe, is generated from this lotus flower. This first-born living being, unlike all the others, has no material father, and thus he is called self-born, or svayambhū. He goes to sleep with Nārāyaṇa at the time of devastation, and when there is another creation, he is born in this way. From this description we have the conception of three — the gross virāṭ form, the subtle Hiraṇyagarbha and the material creative force, Brahmā.