The Lord [Mahā-Viṣṇu], although lying in the Causal Ocean, came out of it, and dividing Himself as Hiraṇyagarbha, He entered into each universe and assumed the virāṭ-rūpa, with thousands of legs, arms, mouths, heads, etc.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स एव पुरुषस्तस्मादण्डं निर्भिद्य निर्गतः । सहस्रोर्वङ्घ्रिबाह्वक्षः सहस्राननशीर्षवान्
sa eva puruṣastasmādaṇḍaṃ nirbhidya nirgataḥ | sahasrorvaṅghribāhvakṣaḥ sahasrānanaśīrṣavān
SB 2.5.35