In Śvetāmbara tradition, the earliest clear references to the Namokar (Navkār) Mantra in literature (not inscriptions) are generally traced to the early canonical texts, especially:

1. Vyākhyāprajñapti (Bhagavatī-sūtra) – Śvetāmbara Āgama

- Scholarly studies on the history of the mantra note that the full five‑fold salutation to the Pañca‑Parameṣṭhi first appears as a maṅgalācaraṇa (auspicious opening) in the condensed/edited form of the Vyākhyāprajñapti. ( en.wikipedia.org) - This places a Śvetāmbara textual attestation (in essentially the current five‑pada form) roughly in the early centuries of the Common Era, though the redaction history of the Āgamas is complex.

1. Avasyaka-sūtra (and its tradition) – Śvetāmbara canonical and post‑canonical layer

- The Avasyaka-sūtra (around 5th century CE in its preserved form) and its commentarial tradition show the Namaskāra formula with slight linguistic evolution (e.g., arahanta → arihanta, use of ṇ/न). ( en.wikipedia.org) - In Śvetāmbara practice, Navkār is tightly connected with Samayika and Avasyaka rituals; many teachers therefore state that, for Śvetāmbaras, the mantra is “as old as the Avasyaka tradition itself.”

1. Pannavana / Prajñapana (Upāṅga Āgama) – Śvetāmbara Upāṅga

- Editorial introductions to the Pannavana-sutta (Prajñapana) point out that early Jaina texts do not always quote the entire five‑pada mantra explicitly, but they treat the pañca‑namaskāra as a known formula. ( jainworld.jainworld.com) - This suggests that by the time Pannavana and allied texts took their present shape, the five‑fold Namaskāra was already established in Śvetāmbara circles, even if not always written out fully.

Summary for your specific question

• Earliest Śvetāmbara literary stratum:

The Namokar formula (at least its core lines) is embedded in the earliest Śvetāmbara Āgamas, with the most explicit early canonical appearance of the full five‑pada form usually assigned to the Vyākhyāprajñapti (Bhagavatī‑sūtra) tradition.

• Later but very influential Śvetāmbara sources:

The Avasyaka-sūtra and its commentaries, and the Pannavana (Prajñapana), give us clearer, more developed Śvetāmbara presentations of the mantra and show that by this period Navkār was already central in daily liturgy.

From the Jain spiritual standpoint, Śvetāmbara as well as Digambara traditions still regard the Navkār Mantra as anādi (beginningless), not “composed” at a historical moment; textual “earliest references” only tell us when it was first written down in surviving Śvetāmbara literature.

For a simple overview of Navkār Mantra and its traditional understanding, you can read more here: