when is the first unequivocal reference to Narasimha, the avatara of Vishnu?

Question

In the ultimate Vaishnavite purana, Vishnu-purana - Narasimha hardly exists. Hiranykashipu repents and Vishnu gives him boons. It is parenthetically mentioned that he was killed by Narasimha, but the "near-invincibility" boon is absent.

Vaishnavite partisans claim to see Narasimha in Rig Veda

I WILL declare the mighty deeds of Viṣṇu, of him who measured out the earthly regions, Who propped the highest place of congregation, thrice setting down his footstep, widely striding. For this his mighty deed is Viṣṇu lauded, like some wild beast, dread, prowling, mountain-roaming; He within whose three wide-extended paces all living creatures have their habitation.

Nothing associates lions with mountains. Whatever this means, it is pure fancy to say that Narasimha appears in Rig Veda.

Answer 1

Saying which is the first reference is difficult unless some deity is mentioned in the Vedas themselves. In that case, the Vedas will be the first reference.

Anyways, there is a minor Upanishad (linked with the Atharva Veda) called Nrisimha Tapaniya. This might be taken as the first mention of the deity if this text can be proved as earlier to the Puranas.

My salutations to that Nrusimha. Who is fierce. Who is heroic. Who is Mahavishnu. Who is burning. Who has faces everywhere. Who is half lion half man.

Answer 2

Though there is no direct reference to Narasimha in vedas, the verse OP quoted can be interpreted as referring to Narasimha with pramanas from Puranas. For direct reference Narasimha tapaniya upanishad would be the first reference.

OP said:

Nothing associates lions with mountains. Whatever this means, it is pure fancy to say that Narasimha appears in Rig Veda.

Narasimha Purana associates Narasimha with mountains as follows: This is from LakshmiNarasimha sahasranama stotram.

पातालस्थितसिंहाय नमः पर्वतवासिने। नमो जलस्थसिंहाय अन्तरिक्षस्थिताय च ॥ ११७॥

Source: sanskritdocuments.org