विविक्त एक आसीन उदिते रविमण्डले ॥ १५ ॥
upaspṛśya jalaṁ śuciḥ
vivikta eka āsīna
Once upon a time he [Vyāsadeva], as the sun rose, took his morning ablution in the waters of the Sarasvatī and sat alone to concentrate.
The river Sarasvatī is flowing in the Badarikāśrama area of the Himālayas. So the place indicated here is Śamyāprāsa in Badarikāśrama, where Śrī Vyāsadeva is residing.