A part of the puruṣa lies down within the water of the universe, from the navel lake of His body sprouts a lotus stem, and from the lotus flower atop this stem, Brahmā, the master of all engineers in the universe, becomes manifest.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यस्याम्भसि शयानस्य योगनिद्रां वितन्वतः । नाभिह्रदाम्बुजादासीद्ब्रह्मा विश्वसृजां पतिः
yasyāmbhasi śayānasya yoganidrāṃ vitanvataḥ | nābhihradāmbujādāsīdbrahmā viśvasṛjāṃ patiḥ
SB 1.3.2