Muslims pray 5 times a day because Allah :swt: asked the prophet :saws: to teach the Ummah to pray 5 times a day. On the night of Mi'raj, Allah :saws: enjoined upon Muslims to pray 5 times a day. Please see the Hadith of Mi'raj mentioned here:
Origins of the 5 daily prayers
The OP seems to be a Quranist. He has to first understand that legislation in Islam is based on
Quran and Sunnah. Allah :swt: does not say in the Qur'an to pray only 3 times a day, nor does He say in the Qur'an how to pray. Allah :swt: sent prophet Muhammad :saws: as a guide to mankind and instructed him to teach the Ummah each and every aspect of their lives. So we learn how to pray and when to pray based on the Sunnah of the Messenger of Allah, :saws:.
Allah (سبحانه وتعالى) says:
... And We revealed to you the message that “you may make clear to the people what was sent down to them” and that they might give thought. [
An-Nahl: 44]
Please see
http://sunnahonline.com/library/bel...-messenger-obey-him-and-follow-his-sunnah-the for more details on why we should follow the Prophet :saws:.
The obligation to obey the prophet (ﷺ):
As for the obligation to obey the prophet (ﷺ), belief in him demands it. Confirmation of what he brought requires obedience to him because this is part of what he brought.
Allah says,
"O you who believe, obey Allah and His Messenger ... " [ 8:20]
"Say: obey Allah and obey the Messenger ... " [ 24:54]
He says,
"Obey Allah and the Messenger and perhaps you will be shown mercy." [3:132]
"If you obey him, you will be guided ... " [ 24:54]
"Whoever obeys the Messenger has obeyed Allah ... " [ 4:79]
"That what the Messenger brings you and leave what he forbids you ... " [ 59:7]
"Whoever obeys Allah and the Messenger is with those whom Allah has blessed."[ 4:68]
"We did not send any Messenger but for him to be obeyed by the permission of Allah." [ 4:63]
He made obeying His Messenger (ﷺ) tantamount to obeying Himself, and He placed obedience to Himself alongside obedience to His Messenger. Allah promises that doing this will result in an abundant reward and threatens a severe punishment for opposing it. He made it obligatory to obey the things that the prophet (ﷺ) commanded and to avoid those he prohibited.
The commentators and Imams have said that obeying the Messenger means to cling to his Sunnah and submit to what he brought. They said that Allah (سبحانه وتعالى) did not send a Messenger without obliging those to whom he was sent to obey him and that obeying the Messenger in his Sunnah is equivalent to obeying Allah (سبحانه وتعالى) in His obligations.
Sahl at-Tustari was asked about the Shari'ah of Islam and he quoted,
"Take what the Messenger brings you." [ 59:7]
As-Samarqandi said that it was said: obey Allah in His obligations and the Messenger in his Sunnah. It is also said: obey Allah regarding what He makes forbidden for you and obey the Messenger regarding what he conveys to you. It is said that it means to obey Allah
(سبحانه وتعالى) by testifying that He is the Lord and to obey the Prophet by testifying to his prophethood.
Abu Salamah ibn 'Abdur-Rahman heard Abu Hurayrah say that the Messenger of Allah said: "Whoever obeys me has obeyed Allah. Whoever rebels against me has rebelled against Allah. Whoever obeys my Amir has obeyed me. Whoever rebels against my Amir has disobeyed me." [Bukhari and Muslim ]
Obeying the Messenger is part of obeying Allah
(سبحانه وتعالى) since Allah commands that he be obeyed. True obedience is obedience to Allah's command and therefore obedience to His Prophet.
Allah
(سبحانه وتعالى) talks about the unbelievers in the depths of the Fire saying, "On the day when their faces are turned over in the Fire, they will say, 'Would that we had obeyed Allah and that we had obeyed the Messenger.' " [ 33:66] They will wish they had obeyed when the wish will not profit them.
The Prophet (ﷺ) said: "When I forbid you to do something, avoid it. When I command you to do something, then do it as much as you are able."[Bukhari and Muslim ]
Abu Hurayrah we find that the Prophet said, "All of my community will enter the Garden except for those who refuse to." They asked, "O Messenger of Allah, who will refuse?" He replied, "Whoever obeys me will enter the Garden. Whoever rebels against me has refused." [Al-Hakim]
The prophet (ﷺ) said: "My likeness and the likeness of what Allah has sent me with is like a man who comes to a people and says, 'O people, I have seen the army with my own eyes and I am a sincere warner, so save yourselves!' One group of his people obey him and they travel at the beginning of the night, go at their leisure and are saved. Another group reject him and remain where they are and the army arrives in the morning and wipes them out. Such is the likeness of those who obey me and follow what I bring and the likeness of those who rebel against me and deny what I bring." [Bukhari]
In an other similar Hadith: "It is like someone who builds a house and lays out a fine feast in it and sends out a summoner. Whoever does not answer the summoner does not enter the house and eat from the feast."[Bukhari and Muslim ]
The obligation to follow him and his Sunnah:
As for the obligation to follow him and obey his Sunnah and follow his guidance, Allah says,
"Say: if you love Allah, follow me and He will love you and forgive you your wrong actions." [ 3:31]
"Believe in Allah and His Messenger, the unlettered prophet who believes in Allah and His words. Follow him, perhaps you will be guided." [ 7:157]
"No, by your Lord, they will not believe until they ask you to judge between them in what they disagree about and then they shall find in themselves no impediment touching your verdict, but shall surrender in full submission." [ 4:64] i.e. obey your judgement.
Allah also says,
"You have a good model in the Messenger of Allah for one who hopes for Allah and the Last Day." [ 33:21]
At-Tirmidhi said, "To take the Messenger as a model means to emulate him, follow his sunnah and abandon opposition to him in either word or action." Several commentators said words to that effect.
In the first ayah mentioned, Allah
(سبحانه وتعالى) promises His love and forgiveness to those who follow the Prophet and prefer him to their own passions and inclinations.
Soundness of belief is based on submission to the Prophet and satisfaction with his judgement and abandoning opposition to him.
It is related from al-Hasan al-Basri that some people said, "Messenger of Allah, we love Allah," so Allah revealed, "
Say: if you love Allah, follow me and Allah will love you." [ 3:31]
Abu Rafi' reported that the prophet (ﷺ) said:
"Do not let any of you be found reclining on his bed when he hears an injunction from me which is from among those things which I myself commanded or forbade so that he says, 'I do not know. We only follow what we find in the Book of Allah.' [Abu Dawud, At-Tirmidhi and Ibn Majah.]
Aisha [ra] said: "The Messenger of Allah (ﷺ) did something as an example in order to make things easier for people but some people still refrained from doing it. When the prophet (ﷺ) heard about that, he praised Allah and said, 'What do you think of people who refrain from anything that I myself do? By Allah, I am the greatest of them in knowledge of Allah and the strongest of them in fear of Allah.' [Bukhari and Muslim ]
Abu Hurayrah said that the prophet (ﷺ) said: "The one who clings to my sunnah when the community is corrupt will have the reward of a hundred martyrs." [At-Tabarani]
Amr ibn Awf al-Muzani said the prophet (ﷺ) told Bilal ibn Al-Harith:"Whoever brings to life any of my Sunnah which has died after me will have the reward of all those who act by it without decreasing their reward in any way. Whoever introduces a misguiding innovation which does not please Allah and His Messenger will have the like of all those who act by it without that decreasing their burden."[At-Tirmidhi, Ibn Majah]