Valmiki Ramayana Bala Kanda Sarga 1 Shloka 80

सरितां पति: lord of rivers, समुद्र: Samudra, आत्मानम् in his own form, दर्शयामास appeared (to Rama), समुद्रवचनात् च एव on the advice of Samudra , नलम् through Nala, सेतुम् a bridge, अकारयत् got it built.

Samudra, lord of rivers, (afraid of Rama's anger) and having appeared in his own form, and on his advice got a bridge built with the help of Nala.