sa kadācit sarasvatyā
upaspṛśya jalaṁ śuciḥ
vivikta eka āsīna
udite ravi-maṇḍale
saḥ - he; kadācit - once; sarasvatyāḥ - on the bank of the Sarasvatī; upaspṛśya - after finishing morning ablutions; jalam - water; śuciḥ - being purified; vivikte - concentration; ekaḥ - alone; āsīnaḥ - being thus seated; udite - on the rise; ravi-maṇḍale - of the sun disc.
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.