AFAIK the evidence is that well known civilian Gulen affiliates were caught in military bases and armoured vehicles on the coup night but a concrete evidence of Gulen himself giving the orders do not exist. A bit like the story of the Russian military personnel in Ukraine(like everything points to Russia but Kremlin denies any involvement and claims that the caught soldiers were on a vacation in war zone).

If you want to read more about the subject, here is a nice write up by pro-Erdogan, liberal, non-islamist(yep, they still exist) Turkish jurnos: https://medium.com/@15thJulyCoup/who-was-behind-the-15th-jul...