Valmiki Ramayana Bala Kanda Sarga 44 Shloka 5
Original Shlokaइयं च दुहिता ज्येष्ठा तव गङ्गा भविष्यति । त्वत्कृतेन च नाम्नाऽथ लोके स्थास्यति विश्रुता।।1.44.5।।
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इयम् this, गङ्गा Ganga, तव your, ज्येष्ठा eldest, दुहिता daughter, भविष्यति will become, अथ from now onwards, त्वत्कृतेन formed out of your, नाम्ना name, लोके in this world, विश्रुता wellknown, स्थास्यति will stay on.
This Ganga will become your eldest daughter and from now on she will be wellknown in this world (as Bhagirathi) after your name.