In the Name of God, Most Gracious, Most Merciful

The question of not having all details of Salah in Quran

How come the details of observing our Contact Prayers are not mentioned in Quran?

The way we observe our Contact Prayers, Salah, is not based on Hadith. Quran teaches us that its rituals were in existence and were delivered and practiced by prophet Abraham way before Quran and prophet Muhammad's time:

[4:125] Who is better guided in his religion than one who submits totally to GOD, leads a righteous life, according to the creed of Abraham: monotheism? GOD has chosen Abraham as a beloved friend.

[22:78] You shall strive for the cause of GOD as you should strive for His cause. He has chosen you and has placed no hardship on you in practicing your religion - the religion of your father Abraham. He is the one who named you "Submitters" originally. Thus, the messenger shall serve as a witness among you, and you shall serve as witnesses among the people. Therefore, you shall observe the Contact Prayers (Salat) and give the obligatory charity (Zakat), and hold fast to GOD; He is your Lord, the best Lord and the best Supporter.

[2:127] As Abraham raised the foundations of the shrine, together with Ismail (they prayed): "Our Lord, accept this from us. You are the Hearer, the Omniscient.
[2:128] "Our Lord, make us submitters to You, and from our descendants let there be a community of submitters to You. Teach us the rites of our religion, and redeem us. You are the Redeemer, Most Merciful.

Muhammad then delivered Quran confirming the fact that he is a strict follower of the religion of Abraham that its rites have been already inherited. The word Millat, used in the following verse means "ways or methods of worship" in the Arabic dictionary. Muhammad followed the rites that were practiced by Abraham:

[16:123] Then we inspired you (Muhammad) to follow the religion of Abraham,* the monotheist; he never was an idol worshiper.

As far as all of our rites, Quran only dealt with whatever got altered since Abraham such as the tone of our prayer (17:110), the basic steps of ablution (5:6), the times of our five daily contact prayers, the command of giving the utmost importance to the Friday Congregational Prayer (62:9), allowing sexual relationship with our spouses during the nights of Ramadan (2:187), whatever is mentioned in regard of Hajj and Umrah, and whatever is mentioned in regard of our Zakat, with the highlight that it is due whenever we collect or receive our income (6:141). Anything in regard of our rituals that is not detailed in Quran has been already preserved by God and passed down correctly and this is basically why it is not detailed in Quran.

Believing in Quran alone mandates the belief in the words stated by God to teach us the above system of how we inherited our rites including of course our contact prayers. This system is spelled out in 16:123, 4:125, 22:78, and 2:127-128. Ignoring this clear system issued by God, and hanging on our personal wishes to find all the details of our rituals in Quran only reflects our disbelief in Quran itself, the lack of trust in its divinity, and the lack of trust in God and His systems. . Indeed, Quran is complete and fully detailed. Part of its complete details is the above system of inheriting our rites from Abraham. Either we believe in it or we choose to be with those who take the word of God partially and conditionally. Do they believe in part of the scripture and ignore other parts (2:85)? Those who do so, are the idol worshipers and dividers in the following verses:

[13:36] Those who received the scripture rejoice in what was revealed to you; some others may reject parts of it. Say, "I am simply enjoined to worship GOD, and never associate any idols with Him. I invite to Him, and to Him is my ultimate destiny."
Divine Authorization of the
Quran's Mathematical Code
[13:37] We revealed these laws in Arabic, and if you ever acquiesce to their wishes, after this knowledge has come to you, you will have no ally, nor a protector, against GOD.

[15:90] We will deal with the dividers.
[15:91] They accept the Quran only partially.
[15:92] By your Lord, we will question them all,
[15:93] about everything they have done.
[15:94] Therefore, carry out the orders given to you, and disregard the idol worshipers.