His name was mentioned in #99 of Dr. Tong's Hebrews Expository.
Zainuddin M. Z. is called the Billy Graham of Muslim.
He secretly became a Christian and got baptized after his Hijrah in Mecca where he saw what he interpreted to be a vision from God, of the Lord Jesus Christ on the cross before Kaaba. He believes that it was how God was telling him to became a Christian. - Paraphrased from Tong.
This revelation is never public even after his death.
I thought to myself, lots of Muslims converting to Christianity because of some supernatural visions in the middle East. Many western conservatives are skeptical of it. I am too. But I am willing to open to the possibility that this is in fact the Lord's direct doing. Direct, meaning not through the act of demons.
However, because of this, it attracted many Charismatics' attention and zeal to aid these new Muslim converts. Resulting in really really bad theology. Therefore, the reformed needs to do more evangelical works than they are currently claiming, this is a rebuke from the Lord, I'm sure.
Now, as for Zainuddin's secrecy in conversion and perhaps even to the extend of cover up, it can only be left to the Lord's mercy, as Naaman did before Elisha.