Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 24: The History of Sarayū
Text 1.24.9
तस्मात्सुस्राव सरसः सायोध्यामुपगूहते।
सरःप्रवृत्ता सरयूः पुण्या ब्रह्मसरश्च्युता॥
tasmāt susrāva sarasaḥ sāyodhyām upagūhate
saraḥ-pravṛttā sarayūḥ puṇyā brahma-saraś-cyutā
tasmāt = from that; susrāva = flowed; sarasaḥ = lake; sā = the river [that]; ayodhyām = Ayodhyā; upagūhate = surround; saraḥ-pravṛttā = [Because] it has come from a lake; sarayūḥ = it is known as Sarayū; puṇyā = it is sacred; brahma-saraḥ-cyutā = for it has descended from Lord Brahmā’s lake.
The river [that] flowed from that lake surrounds Ayodhyā. [Because] it has come from a lake, it is known as Sarayū. It is sacred for it has descended from Lord Brahmā’s lake.
Sarayū surrounded and flowed around Ayodhyā. It came around the western side of Ayodhyā, moved around its northern side, reached its eastern side and then reached Aṅgadeśa and joined with Gaṅgā. At the confluence of the two rivers was the āśrama of Sthāṇu or Lord Rudra. While crossing over Gaṅga merged with the Sarayū, a sound was heard because Sarayū flowed from a higher plane onto the Bhāgīrathī.
Viśvāmitra explains the etymological meaning of Sarayū—that which has come out (yū) from the lake (saras).