Ramayana
नीलाः किल पुरा बर्हा मयूराणां नराधिप । सुराधिपाद्वरं प्राप्य गताः सर्वे ऽपि बर्हिणः ॥ 7-18-25 ॥
O king, formerly the feathers of peacocks were blue; and having obtained a boon from the lord of the gods, all the peacocks departed.
english translation