SB 10.89.48

In that darkness the chariot's horses—Śaibya, Sugrīva, Meghapuṣpa and Balāhaka—lost their way. Seeing them in this condition, O best of the Bhāratas, Lord Kṛṣṇa, the supreme master of all masters of yoga, sent His Sudarśana disc before the chariot. That disc shone like thousands of suns. KB 10.89.48-49 When Kṛṣṇa approached the covering layer of this universe, the four horses which were drawing His chariot—Śaibya, Sugrīva, Meghapuṣpa and Balāhaka—all hesitated to enter the darkness. This hesitation is also a part of the pastimes of Lord Kṛṣṇa because the horses of Kṛṣṇa are not ordinary; it is not possible for ordinary horses to go all over the universe and then enter into its outer covering layers. As Kṛṣṇa is transcendental, His chariot and His horses and everything about Him are also transcendental, beyond the qualities of this material world. We should always remember that Kṛṣṇa was playing the part of an ordinary human being, and His horses also, by the will of Kṛṣṇa, played the parts of ordinary horses in hesitating to enter the darkness. Kṛṣṇa is known as Yogeśvara, as stated in the last portion of the Bhagavad-gītā. Yogeśvaro hariḥ: all mystic powers are under His control. In our experience we can see many human beings who have yogic mystic power and who sometimes perform very wonderful acts, but Kṛṣṇa is understood to be the master of all mystic power. Therefore, when He saw that His horses were hesitant to proceed into the darkness, He immediately released His disc, known as the Sudarśana cakra, which illuminated the sky a thousand times brighter than sunlight. The darkness of the covering of the universe is also a creation of Kṛṣṇa’s, and the Sudarśana cakra is Kṛṣṇa’s constant companion. Thus He penetrated the darkness by keeping the Sudarśana cakra before Him.