Go to any of the three springs (courage in faron, power in akkala, and wisdom on mount lanayru) and they will say that something is wrong with the mother goddess statue.
Go to the forgotten temple, interact with the goddess statue, then go back to the one that told you something was wrong with it. After that it will ask for a dragon material, just get that and offer it to the goddess statue.
Do this for each spring, and then you'll get a special item from the mother goddess statue