As quran commanded for the prayer now question is who will teach that how to pray none other than Rasul saw it is a practical act as Allah said in quran
لَّقَدْ كَانَ لَكُمْ فِي رَسُولِ اللَّهِ أُسْوَةٌ حَسَنَةٌ لِّمَن كَانَ يَرْجُو اللَّهَ وَالْيَوْمَ الْآخِرَ وَذَكَرَ اللَّهَ كَثِيرًا
Certainly you have in the Apostle of Allah an excellent exemplar for him who hopes in Allah and the latter day and remembers Allah much.
Sura ahzab ayah 33
When quran said establish the prayer rasul the role model and teacher he said صلو كما رايتموني
Pray the way I'm praying and Rasul saw he used to pray with hand by side
And our chain is not broken after him all our imams they offered in same manner then our maraje and ulama
Our other brothers they are praying in four different ways and no one has claim that it is musalla of Rasul saying that following imam Abu Haneefa or Abu Malik or Shafai or Imam Humbal but we are having 12 Imams and praying the way Rasul offered so all offered in same manner .
In quran no of Rakat of salat and the other methods are not mentioned. Allah sent the Rasul saw to show the practical