Valmiki Ramayana Sundara Kanda Sarga 12 Shloka 24

वानरेन्द्राणाम् of the great vanara, उद्योगम् effort, सागरस्य ocean's, प्लवनं च in crossing, व्यर्थम् wasted, वीक्ष्य after seeing that, अनिलसुतः son of the Windgod, पुनः again, चिन्ताम् worry, उपागमत् experienced.

The son of the Wind god, the great monkey realised the futility of his efforts in crossing the sea. He brooded again.