Muslims perform their prayers by facing the Qibla —or the direction to the Kaaba in Mecca, Saudi Arabia. The Qibla direction is traditionally determined from the direction to the Sun when the Sun is directly overhead the Kaaba. If the Sun is visible during that time, it will indicate the direction of the Qibla.
If the observation results are drawn on the so-called ‘flat-Earth map,’ the Qibla will not consistently point to the Kaaba. Only calculations using the spherical Earth model will give us consistent results that agree with centuries of observation from various locations on Earth. The Qibla proves Earth is a sphere.