 Al-Ghazali was his name, who was to Islam what St. Augustine was to Christianity. St. Augustine kind of laid out the rules for how to be a good Christian at the time. A lot of people were practicing it in their own way. He codified it. He was a religious scholar, figured it out according to his own read, told everybody how to behave. There's the book. You follow this, you're a good Christian. Al-Ghazali said, you follow this, you're a good Muslim.