Purāṇas · c. 3rd-5th c. CE
दिविच्छायापथो यस्तु अनुनक्षत्रमण्डलम् । दृश्यते भास्वरो रात्रौ देवी त्रिपथगा तु सा ।। ४७.२८ ।।
...seen shining at night — she is the goddess Tripathagā. — Literal rendering by the compiler
Not a separate object but the identification supplied by the same verse: the chāyāpatha IS Tripathagā, i.e. the celestial Gaṅgā. This is the Purāṇic equation of the Milky Way with the sky-river, stated rather than inferred. Distinct from Mandākinī, which in these same texts is always a terrestrial Himalayan river and never a sky-object.
Vāyu Purāṇa 47.28; Brahmāṇḍa Purāṇa 1,18.29; Matsya Purāṇa 121.29-30 · text · translation