Salah is the practice of formal worship in Islam. Its importance for Muslims is indicated by its status as one of the Five Pillars of Islam. Salah is a ritual worship, having prescribed conditions, a prescribed procedure, and prescribed times. To perform valid Salah, Muslims must be in a state of ritual purity, which is mainly achieved by ritual ablution, (wuḍūʾ), according to prescribed procedure
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Salah is prescribed at five periods of the day. These are measured according to the movement of the sun. These are: near dawn (fajr – 2 rakats), after midday has passed and the sun starts to tilt downwards / Noon (dhuhr or ẓuhr – 4 rakats), in the afternoon (asr – 4 rakats), just after sunset (maghrib – 3 rakats) and around nightfall (‘isha – 4 rakats), hence 2-4-4-3-4.

Abu Huraira radiyallahu ʿanhu narrates that I heard Allah’s Apostle saying, “If there was a river at the door of anyone of you and he took a bath in it five times a day would you notice any dirt on him?” They said, “Not a trace of dirt would be left.” The Prophet added, “That is the example of the five prayers with which Allah blots out (annuls) evil deeds.” —Sahih al-Bukhari.