Bhagavatapurana 3.26.25

3.26.25

sahasra-śirasaṃ sākṣād yam anantaṃ pracakṣate /
saṅkarṣaṇākhyaṃ puruṣaṃ bhūtendriya-manomayam //

25. (And in these the Lord's form to be contemplated is) the Purusha called Sankarshana who has a thousand heads who presides over the Bhutas, the organs and the minds and whom they directly speak of as Ananta.