Canto 2 -
Ayodhyā-kāṇḍa
Chapter 45: The Brāhmaṇas from Ayodhyā Follow Rāma
Text 2.45.32

एवं विक्रोशतां तेषां द्विजातीनां निवर्तने।
ददृशे तमसा तत्र वारयन्तीव राघवम्॥

evaṁ vikrośatāṁ teṣāṁ dvi-jātīnāṁ nivartane
dadṛśe tamasā tatra vārayantīva rāghavam

evam = in this manner; vikrośatām = were crying; teṣām = while those; dvi-jātīnām = twice-born; nivartane = to stop [Rāma’s departure]; dadṛśe = was seen; tamasā = the river Tamasā; tatra = there; vārayantī iva = it seemed to prevent [from going further]; rāghavam = Rāghava.

While those twice-born were crying in this manner to stop [Rāma’s departure], the river Tamasā was seen there.1 It seemed to prevent Rāghava [from going further].  

1 While Rāma and the others were walking, they noticed the river Tamasā ahead, flowing across the path.