What more do you need?
He said the Muslim call to prayer in perfect Arabic to Kristof. The call to prayer is an avowal of Muslim faith. To say it aloud is to declare oneself a Muslim.
He's obviously practiced at it.
I'm certainly no expect on styles of Arabic calligraphy, but this story of Zero's ring, if confirmed by other experts, pretty much seals the deal.
Our president is a Muslim. But not just a Muslim, but a Muslim who practices taquiya and other “allowed” deceptions.