He (Vijitasva) received this title from Indra, and it refers to the time when Indra stole Maharaja Prthu's horse from the sacrificial arena. Indra was not visible to others when he was stealing the horse, but Maharaja Prthu's son Vijitasva could see him

Expressions researched:
"He received this title from Indra, and it refers to the time when Indra stole Mahārāja Pṛthu's horse from the sacrificial arena. Indra was not visible to others when he was stealing the horse, but Mahārāja Pṛthu's son Vijitāśva could see him"

Srimad-Bhagavatam

SB Canto 4

Mahārāja Vijitāśva was known as Antardhāna, which means "disappearance." He received this title from Indra, and it refers to the time when Indra stole Mahārāja Pṛthu's horse from the sacrificial arena. Indra was not visible to others when he was stealing the horse, but Mahārāja Pṛthu's son Vijitāśva could see him. Yet despite his knowing that Indra was taking away his father's horse, Vijitāśva did not attack him. This indicates that Mahārāja Vijitāśva respected the right persons.

SB 4.24.3, Translation and Purport

Formerly, Mahārāja Vijitāśva pleased the King of heaven, Indra, and from him received the title Antardhāna. His wife's name was Śikhaṇḍinī, and by her he begot three good sons.

Mahārāja Vijitāśva was known as Antardhāna, which means "disappearance." He received this title from Indra, and it refers to the time when Indra stole Mahārāja Pṛthu's horse from the sacrificial arena. Indra was not visible to others when he was stealing the horse, but Mahārāja Pṛthu's son Vijitāśva could see him. Yet despite his knowing that Indra was taking away his father's horse, Vijitāśva did not attack him. This indicates that Mahārāja Vijitāśva respected the right persons. Although Indra was stealing the horse from his father, Vijitāśva knew perfectly well that Indra was not an ordinary thief. Since Indra was a great and powerful demigod and servant of the Supreme Personality of Godhead, Vijitāśva purposefully excused him due to sentiment only, even though Indra was acting wrongly. Thus Indra became very pleased with Vijitāśva at that time. The demigods have the great mystic power of being able to appear and disappear according to their will, and since Indra was very pleased with Vijitāśva, he bestowed this mystic power upon him. Thus Vijitāśva became known as Antardhāna.