Valmiki Ramayana Bala Kanda Sarga 38 Shloka 13

रघुनन्दन O One causing delight to the descendents of Raghu, राम Rama , मुने: ascetic's, वचनम् words, श्रुत्वा having heard, केशिनी Kesini, वंशकरम् perpetuating the race, पुत्रम् son, नृपसन्निधौ in the presence of king, जग्राह accepted.

"O Rama, delight of the descendants of Raghus, on hearing the words of the ascetic in the presence of king Sagara, Kesini chose the boon to have a son who perpetuates the race.