Canto 2 -
Ayodhyā-kāṇḍa
Chapter 18: Kaikeyī Informs Rāma About the two Boons
Text 2.18.7

अचिन्त्यकल्पं हि पितुस्तं शोकमुपधारयन्।
बभूव संरब्धतरः समुद्र इव पर्वणि॥

acintya-kalpaṁ hi pitus taṁ śokam upadhārayan
babhūva saṁrabdhataraḥ samudra iva parvaṇi

acintya-kalpam hi = it was impossible; pituḥ = for his father; tam = in this manner; śokam = to lament; upadhārayan = thinking that; babhūva = He became; saṁrabdhataraḥ = even more perplexed; samudraḥ = the ocean; iva = like; parvaṇi = on a Pūrṇimā.

Thinking that it was impossible for His father to lament in this manner, He became even more perplexed, like the ocean on a Pūrṇimā.1 

1 He thought that it was naturally impossible for Daśaratha to lament in this manner.