Source: TW
Someone asked what the earliest attestation of connection between garuDa and viShNu was; I think:
viShNave tvA shyenAya tvA somabhR^ite viShNave tvA |
from yajurvedic texts.
There is another connection between the two seen in the paippalAda shruti which might be coeval too.
In the maitrAyaNIya saMhitA the incantation of the two are juxtaposed. The first incantation describes the “ritual” form of garutmant:
सु॒प॒र्णो॑ऽसि ग॒रुत्मा᳚न् , त्रि॒वृत्ते॒ शिरो॑ गाय॒त्रञ्चख्षु॒स् स्तोम॑ आ॒त्मा साम॑ ते त॒नूर्वा॑मदे॒व्यम् बृ॑हद्रथन्त॒रे प॒ख्षौ, य॑ज्ञाय॒ज्ञिय॒म्पुच्छ॒ञ्, छन्दा॒ँ॒स्यङ्गा॑नि॒, धिष्णि॑याश्श॒फा, यजूँ॑षि॒ नाम॑ ।
सु॒प॒र्णो॑ऽसि ग॒रुत्मा॒न् , दिव॑ङ्गच्छ॒ सुव॑ᳶ पत ॥ viShNoH kramo.asi sapatnahA gAyatraM ChandA Aroha pR^ithivIm anuvikramasva viShNoH kramo.asyabhimAtihA traiShTubhaM ChandA Aroha antarikSham anuvikramasva viShNoH kramo.asyarAtIyato hantA jAgataM ChandA Aroha, divam anuvikramasva viShNoH kramo.asi shatrUyato hantA AnuShTubhaM ChandA Aroha disho.anuvikramasva ||
The chant of the foe-slaying strides of viShNu is coupled with that of the flight of suparNa to the heavens.