CC Ādi 5.100-101
sahasra mastaka tāṅra sahasra vadana
In the reservoir of water first created by the perspiration of Garbhodakaśāyī Viṣṇu, the Lord lies on the Śeṣa plenary expansion of Viṣṇu, who is described in Śrīmad-Bhāgavatam and in the four Vedas as follows:
sahasra-śīrṣā puruṣaḥ sahasrākṣaḥ sahasra-pāt
sa bhūmiṁ viśvato vṛtvā- tyatiṣṭhad daśāṅgulam
The Viṣṇu form called Ananta-śayana has thousands of hands and legs and thousands of eyes, and He is the active generator of all the incarnations within the material world.