Which is the earliest scripture to describe physical attributes of Vishnu?

Question

In the Rig Veda the God called Vishnu has only two characteristics - he is large and is a youth. When are attributes such as shanka, chakra etc. associated with him?

Answer 1

Narayana suktam tells some physical attributes-

nīlatoyadamadhyasthād vidyullekheva bhāsvarā, nīvāraśūkavattanvī pītā bhāsvatyaṇūpamā.

Brilliant like a streak of lightning set in the midst of the blue rain-bearing clouds, slender like the awn of a paddy grain, yellow (like gold) in colour, in subtlety comparable to the minute atom, glows splendid.

Skin colour like rain bearing cloud, slender- and golden tint due to being srinivasa.

Shatpatha brahmana mentions Vishnu the son of aditi (vamana) as a dwarf taking over 3 worlds

They then said: "Let us share in this earth along with yourselves! Let a part of it be ours!" The Asuras replied rather grudgingly: 'As much as this Vishnu lies upon, and no more, we give you!' Now Vishnu was a dwarf.... By it they obtained (sam-vid) this entire earth; and because they obtained by it this entire (earth), therefore it (the sacrificial ground) is called vedi (the altar).