The prescribed prayer is a worship starting with takbeer (saying Allah is the Greatest) and finishing with salam (salutation) and containing some specific acts and words. It is an expression of glorification, exaltation and praise toward Allah.
Five daily prayers/Salat are mentioned in more than ninety verses in the Qur'an. There were not five daily prayers (like in Islam) in former Shari'as (religious laws system). However there was a kind of prayer that has no appointed times. Five daily prayers were prescribed one and half years before the Hegira (Migration) on the night of Ascension of the Prophet Muhammad (Peace and Blessing be upon Him). According to a narration of Anas bin Malik, he stated the following as a summary:
“The five daily prayers were prescribed to the Prophet Muhammad as fifty times a day on the night of the Ascension. Then, they were decreased to five times a day. Then the Prophet Muhammad (PBUH) was addressed as follows (by Allah), "O Muhammad! Our order has not changed. These five daily prayers are equivalent to fifty daily prayers for you. (Bukhari, the Prayers, 76, Anbiya,5; Muslim, Belief, 263; Ahmed bin Hanbal, V,122,143). It is determined with the following verse that tenfold reward is given for each good action; "Whoever comes with a good deed, he will be rewarded with tenfold. (Al-An'am, 6/160; also An-Naml, 27/89;Al-Qasas, 28/84). Before the five daily prayers were prescribed, the Prophet Muhammad (PBUH) used to worship Allah by meditating on the creatures of Allah and His Dignity. It is also narrated that he performed two rak'ah prayers in the mornings and evenings. Former communities also had the worship of prayers (salah). Here are some examples from the Qur’an; Luqman (Peace be upon him) ordered the prayers to his son (Luqman,31/17). When the Prophet Abraham was supplicating to Allah for the security of Hejaz, he mentioned about the prayers (Abraham,14/37). Almighty Allah wanted the prophet Moses to perform the prayers during the first revelation of him (Ta-Ha, 20/14).
The legitimacy of five daily prayers is based on the Scripture (the Quran), the Practices of the Prophet Muhammad(PBUH), and Consensus (the acceptance of all Islamic scholars and Companions of the Prophet Muhammad (PBUH)).
Performing the prayers and giving the zakat/alms is ordered in the many verses of the Qur’an. “Guard strictly your (habit of) prayers Especially the middle prayer”(al-Baqara, 2/238). For such prayers are enjoined on believers at stated times (An-Nisa, 4/103).
And they have been commanded no more than this: to worship Allah, offering Him sincere devotion, being True (in faith); to establish regular Prayer; and to practise regular Charity; and that is the Religion Right and Straight (Al-Bayyina, 98/5). So establish regular Prayer give regular Charity, and hold fast to Allah! He is your Protector― the― Best to protect and the Best to help (Al-Hajj, 22/78).
Evidences from the Practices of the Prophet Muhammad (PBUH); there are many hadiths narrated about this topic. Some of them are as follows: According to what is narrated from Ibn Umar, the Prophet Muhammad (PBUH) said, "Islam is founded on five principles; testifying that there is no god but Allah and the Prophet Muhammad is His Messenger, performing the prayers, giving alms (zakah) pilgrimage to the Kaaba and fasting in Ramadan (Bukhari, Belief, 1,2; Muslim, Belief, 19-22).
Prophet Muhammad (PBUH) said the following to Muadh bin Jabal when sending him to Yemen; “You are going to a community that is from the people of the Book. Firstly, invite them to worship Allah. If they accept Allah, proclaim them that Allah prescribed you five daily prayers in a day. If they accept the prayers, proclaim them that Allah prescribed the zakat/alms to them to be given to the poor people from the rich ones. If they obey this, take it from them, (but) do not take the best goods of people; and avoid from the maledictions of the oppressed people because there is no barrier between the prayer of the oppressed person and Allah (Bukhari, Zakat, 41, 63, Maghazi, 60, Tawhid, 1; Nasai, Zakat, 1; Darimi, Zakat,I).
On the other hand, the Islamic community agree unanimously five daily prayers is fard (obligatory).
The five daily prayers is prescribed for each sane Muslim who has reached the age of puberty. However, children who are seven years old are commanded to perform the prayers. When they become ten years-old and do not perform the prayers, they can be beaten slightly. The prophet Muhammad (PBUH) said, “Command your children to perform the prayers when they are seven years old. When they become ten years old and do not perform the prayers, beat them; and separate their beds at this age (Abu Dw’ud, Salat, 26; Ahmad bin Hanbal, II, 180, 187).
The number of the obligatory prayers in a day is five. Only the eid prayers, and witr prayer are wajib. The following hadith about a bedouin is the evidence of the five daily fard prayers; “During a day and night, the number of the prescribed prayers is five. When the bedouin asked ‘Are there any other obligations on me?’ The prophet answered:
“No, you do not have any other obligations except what you perform as supererogatory. Then, the bedouin said, ‘I swear by Allah that I will neither decrease nor increase them. Thereupon,, our Prophet (PBUH) said, "If he has told the truth (performs what he says), he will attain salvation (Bukhari, Belief, 34, Testifying, 26; Muslim, Belief,8,10,15,17,18; Abu Dawud, The Prayers,1)