Avoid Multiple time Submit button click event

<asp:Button ID="btnSubmit" runat="server" class="btn btn-success"  OnClick="btnSubmit_Click"
                      ValidationGroup="Submit" Text="Submit" OnClientClick="if (!Page_ClientValidate()){ return false; } this.disabled = true; this.value = 'Saving...';"
   UseSubmitBehavior="false"></asp:Button>