There are people who spend their lives working with others to examine the world and how it works. They check their ideas as many ways as they can think of and try to build a system of ideas consistent with each other and checked by many other people. They hope their ideas will be useful.
The people who study the shape, position, movement, and other characteristics of earth are astronomers. Astronomy is useful for navigation, since quite long ago it works. Example, the north star inclination above horizon is equal to your latitude. This is one implication of round earth. Works for Muslim navigators, Christians, atheists, anyone.
Muslim scholars spend their time reading the Koran, Haddith, thinking and discussing religion. If I wanted yo know what is in the Koran, I should go to a Muslim scholar, the Koran, or Haddith. If I want to know how gps works, how to do astral navigation works, the size and shape of the earth, etc, I would not go to a Muslim scholar or the Koran, I would ask a scientist. And since scientists can tell me how to navigate, predict eclipses, and give me a coherent story of how all this works together, I would believe them. It works, they can explain it, and it makes sense as a system.