Salah

Salah (Arabic: صلاة ṣalāh or ṣalāt; pl. صلوات is the practice of formal worship in Islam. Its importance for Muslims is indicated by its status as one of the Five Pillars of Sunni Islam, of the Ten Practices of the Religion of Twelver Shiʿi Islam and of the seven pillars of Mustaʿlī Ismaili Islam, with a few dispensations for those for whom it would be difficult. People who find it physically difficult can perform Salah in a way suitable for them. To perform valid Salah, Muslims must be in a state of ritual purity, which is mainly achieved by ritual ablution, (wuḍūʾ), according to prescribed procedures.
Under the Hanbali School of thought, a person who doesn't pray 5 times a day is a disbeliever. The other 3 schools of thought say that the person who doesn't pray 5 times a day is just a sinner. Prayer is regarded as a dividing line between a believer and a non-believer (according to Sahih Muslim).
Salah consists of the repetition of a unit called a rakʿah (pl. rakaʿāt) consisting of prescribed actions and words. The number of obligatory (fard) rakaʿāt varies from two to four according to the time of day or other circumstances (such as Friday congregational worship, which has two rakaʿāt). The minimal,obligatory rakaʿāt may be supplemented with acts that are optional but are considered meritorious. Prayer is wajib (obligatory) for all Muslims except those who are retarded, pre-pubescent, sick, lactating, pregnant, menstruating, frail and elderly or travelling on a long journey.
For Muslims of the Sunni and Ismaili Mustaʿlī persuasions, obligatory salah is prescribed at five periods of the day. These are measured according to the movement of the sun. These are: near dawn (fajr), after midday has passed and the sun starts to tilt downwards / Noon (dhuhr or ẓuhr), in the afternoon (asr), just after sunset (maghrib) and around nightfall ('isha'). Under some circumstances ritual worship can be shortened or combined (according to prescribed procedures). In case a ritual worship is not performed at the right time, it must be performed later. Muslim doctrine permits ẓuhr (ظهر, "noon") and ʿaṣr (عصر, "afternoon") prayers to be performed in succession.