तस्य रामस्य of Rama, सौमित्रिणा सह along with Lakshmana, एवम् in that way, कथयमानस्य as he was narrating, सूर्यः Sun, अस्तं गतः had set, सन्ध्याकालः evening time, अभ्यवर्तत had set in.

While Rama was thus narrating to Lakshmana (the story of Agastya), the Sun set and evening closed in.