The Lord (Krsna) offered His services to His teacher, Sandipani Muni, and the muni, knowing the power of the Lord, asked something which was impossible to be done by anyone else
SB Canto 3
The Lord learned all the Vedas with their different branches simply by hearing them once from His teacher, Sāndīpani Muni, whom He rewarded by bringing back his dead son from the region of Yamaloka.
No one but the Supreme Lord can become well versed in all the branches of Vedic wisdom simply by hearing once from his teacher. Nor can anyone bring a dead body back to life after the soul has already gone to the region of Yamarāja. But Lord Kṛṣṇa ventured to the planet of Yamaloka and found the dead son of His teacher and brought him back to his father as a reward for the instructions received. The Lord is constitutionally well versed in all the Vedas, and yet to teach by example that everyone must go to learn the Vedas from an authorized teacher and must satisfy the teacher by service and reward, He Himself adopted this system. The Lord offered His services to His teacher, Sāndīpani Muni, and the muni, knowing the power of the Lord, asked something which was impossible to be done by anyone else. The teacher asked that his beloved son, who had died, be brought back to him, and the Lord fulfilled the request. The Lord is not, therefore, an ingrate to anyone who renders Him some sort of service. The devotees of the Lord who always engage in His loving service are never to be disappointed in the progressive march of devotional service.