Valmiki Ramayana Bala Kanda Sarga 38 Shloka 14
Original Shlokaषष्ठिं पुत्रसहस्राणि सुपर्णभगिनी तदा। महोत्साहान् कीर्तिमतो जग्राह सुमति: सुतान्।।1.38.14।।
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तदा then, सुपर्णभगिनी sister of (Garuda) Suparna, सुमति: Sumati, महोत्साहान् possessing great perseverance, कीर्तिमत: endowed with fame, षष्ठिम् sixty, पुत्रसहस्राणि thosands of sons, सुतान् as her sons, जग्राह accepted.
Then, Sumati (the other wife) sister of Suparna (Garuda) obtained the boon of sixty thousand sons endowed with fame and great perseverance.