How did Garuda become the vehicle of Vishnu?

Question

While roaming in the Dandaka Forest, Sri Rama visits the hermitage of Sage Agastya. There he comes across various places for offering prayers to important Gods through Agni (Fire.).

He saw that Garuda was worshippped alongwith Vishnu.

स तत्र ब्रह्मणः स्थानम् अग्नेः स्थानम् तथैव च || ३-१२-१७ विष्णोः स्थानम् महेन्द्रस्य स्थानम् चैव विवस्वतः | सोम स्थानम् भग स्थानम् स्थानम् कौबेरम् एव च || ३-१२-१८ धातुर् विधातुः स्थानम् च वायोः स्थानम् तथैव च | स्थानम् च पाश हस्तस्य वारुणस्य महात्मनः || ३-१२-१९ स्थानम् तथैव गायत्र्या वसूनाम् स्थानम् एव च | स्थानम् च नागराजस्य गरुड स्थानम् एव च || ३-१२-२० कार्तिकेयस्य च स्थानम् धर्म स्थानम् च पश्यति |

Rama entered inside the hermitage and saw therein the sanctus of Brahma, Fire-god, Vishnu, Indra, Vivasvat - the Sun-god, Soma - the Moon-god, Bhaga - one among the twelve Suns, and the sanctusms of Kubera, [Wealth-Management-god, are seen and passed by the three of them, sanctums of Dhaata, Vidhaata - Vedic deities created by Brahma to help Svayambhuu Manu, santucm of Vaayu - the Air-god, and also like that the sanctum of great-soloed VaruNa - the Rain-god who also wields noose, and the sanctum of Gayatri - the presiding deity of gnosis, sanctum of Vasus - eight of them, and the sanctum of cobra's king - aadi sheSa, the divine Thousand-headed serpent that bears this globe on its head, and on which Vishnu reclines, and even the sanctum of GaruDa - the Divine Eagle and the vehicle of Vishnu, and the half brother of aadi sheSa, and the sanctum of Kaartikeya - chief of gods army, second son of Shiva, and the sanctum of Dharma - Dharmaraaja, presiding deity of Virtue-Vice-Time of living beings, in-charge of the hell.

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Then a question arises when and how Garuda became the vehicle of Vishnu?

Answer 1

This story is described in the Mahabharata, Adi Parva, Chapter 33:

Then the mighty son of Vinata, taking up the Amrita from the place where it was kept, rose on his wings with great speed, breaking into pieces the machine that had surrounded it. And the bird soon came out, taking the Amrita but without drinking it himself. And he then wended on his way without the least fatigue, darkening the splendour of the Sun. And the son of Vinata then met Vishnu on his way along the sky. And Narayana was gratified at that act of self-denial on the part of Garuda. And that deity, knowing no deterioration, said unto the ranger of the skies, 'O, I am inclined to grant thee a boon.' The ranger of the skies thereupon said, 'I shall stay above thee.' And he again spake unto Narayana these words, 'I shall be immortal and free from disease without (drinking) Amrita.' Vishnu said unto the son of Vinata, 'Be it so.' Garuda, receiving those two boons, told Vishnu, 'I also shall grant thee a boon; therefore, let the possessor of the six attributes ask of me.' Vishnu then asked the mighty Garuda to become his carrier. And he made the bird sit on the flagstaff of his car, saying, 'Even thus thou shalt stay above me.' And the ranger of the skies, of great speed, saying unto Narayana, 'Be it so,' swiftly wended on his way, mocking the wind with his fleetness.