SB 10.2.16

bhagavān api viśvātmā
 bhaktānām abhayaṅkaraḥ
āviveśāṁśa-bhāgena
 mana ānakadundubheḥ
Synonyms: 
bhagavān — the Supreme Personality of Godhead; api — also; viśvātmā — the Supersoul of all living entities; bhaktānām — of His devotees; abhayam-karaḥ — always killing the causes of fear; āviveśa — entered; aṁśa-bhāgena — with all of His potent opulences (ṣaḍ-aiśvarya-pūrṇa); manaḥ — in the mind; ānakadundubheḥ — of Vasudeva.
Translation: 
Thus the Supreme Personality of Godhead, who is the Supersoul of all living entities and who vanquishes all the fear of His devotees, entered the mind of Vasudeva in full opulence.
Purport: 

The word viśvātmā refers to one who is situated in everyone’s heart (īśvaraḥ sarva-bhūtānāṁ hṛd-deśe ’rjuna tiṣṭhati). Another meaning of viśvātmā is “the only lovable object for everyone.” Because of forgetfulness of this object, people are suffering in this material world, but if one fortunately revives his old consciousness of loving Kṛṣṇa and connects with Viśvātmā, one becomes perfect. The Lord is described in the Third Canto (3.2.15) as follows: parāvareśo mahad-aṁśa-yukto hy ajo ’pi jāto bhagavān. Although unborn, the Lord, the master of everything, appears like a born child by entering the mind of a devotee. The Lord is already there within the mind, and consequently it is not astonishing for Him to appear as if born from a devotee’s body. The word āviveśa signifies that the Lord appeared within the mind of Vasudeva. There was no need for a discharge of semen. That is the opinion of Śrīpāda Śrīdhara Svāmī and Śrīla Viśvanātha Cakravartī Ṭhākura. In the Vaiṣṇava-toṣaṇī, Śrīla Sanātana Gosvāmī says that consciousness was awakened within the mind of Vasudeva. Śrīla Vīrarāghava Ācārya also says that Vasudeva was one of the demigods and that within his mind the Supreme Personality of Godhead appeared as an awakening of consciousness.