Valmiki Ramayana Bala Kanda Sarga 21 Shloka 16

पुरा formerly, जया नाम named Jaya, असुरसैन्यानाम् for asura army, वधाय for the destruction, अमेयान् immeasurable prowess, कामरूपिण: possessing power of changing forms at free will, वरान् boon, पञ्चाशतम् fifty, सुतान् sons, लेभे obtained.

Formerly Jaya, for the destruction of the army of asuras gave birth to fifty sons by virtue of a boon. They possess immeasurable power of changing forms at will.