The World Federation One Stop Fiqh

Ruling 722

If a person doubts (i.e. has a shakk) whether the sun has set or not and deems it probable that it is hidden behind mountains, buildings, or trees, he must not perform the maghrib prayer before the redness of the sky in the east – which appears after sunset – has passed overhead. Even if one does not have such a doubt, he must, based on obligatory precaution, wait until the aforementioned time.