Is sunnah prayer from Allah or from muhammad (saw), because it is called sunnah and sunnah is related to muhammad ( saw).
In The Qu'ran it is mentioned more than once about obeying the Messenger of Allah (s.a.w) as a means of obeying Allah, Himself, and how can one possibly obey the Messenger of Allah and follow his example (s.a.w) without first following his sunnah? and this includes the sunnah prayers. However, sunnah is optional apart from where the Prophet (s.a.w) has made certain acts obligatory.
Firstly we should correct the obligatory acts (ie 5 daily prayers etc) then start to follow them up by the sunnah (optional) acts for extra reward and Allah knows best.
Obey Allah, and obey the Messenger, and beware (of evil): if ye do turn back, know ye that it is Our Messenger's duty to proclaim (the Message) in the clearest manner (Qu'ran 5:92)
O ye who believe! obey Allah, and obey the Messenger, and those charged with authority among you. If ye differ in anything among yourselves, refer it to Allah and His Messenger, if ye do believe in Allah and the Last Day: that is best, and most suitable for final determination. (Qu'ran 4:59)
Say: “Obey Allah, and obey the Messenger: but if ye turn away, he is only responsible for the duty placed on him and ye for that placed on you. If ye obey him, ye shall be on right guidance. (Qu'ran 24:54)
And whoever obeys Allâh and His Messenger, Allâh shall admit him in the Gardens underneath which rivers flow. (Qu'ran 4:13)
And whoever obeys Allâh and His Messenger, he has won a great success. (Qu'ran 33:71)
And we sent no messenger, but that he should be obeyed by the leave of Allâh. (Qu'ran 4:64)
There's many more also. I have only mentioned a few on here to get to the point. So from these, we can see clearly that 1) Allah commands us to obey Him and His messenger (s.a.w) and the scholars 'those charged with authority among you' 2) we are responsible for our own actions. The prophet (s.a.w)'s duty is only to convey to us the message in the clearest manner in this instance.
The fact that The Qu'ran is Allah's words, not the prophet's (s.a.w) words, also proves that the only way we can obey His messenger is by following his example via the sunnah. Anything that the Prophet Muhammad (s.a.w) teaches and the examples he laid out for us to follow, if it contradicts The Qu'ran then it's a weak hadith and thus we should not follow that particular hadith as it's likely been forged and not really from the Prophet (s.a.w), however if a particular act of the Prophet (s.a.w) and his sunnah doesn't contradict The Qu'ran's teachings then we should follow it alongside The Qu'ran's teachings. A grading can also be found alongside the hadith as to whether it's a strong/weak hadith.
Always doing the regular Sunnah prayers in particular, and virtuous deeds in general, is something that is recommended in Islamic teaching. The Prophet (s.a.w) was asked: Which deed is dearest to Allah? He said: “That which is done persistently, even if it is little.” Narrated by al-Bukhaari (6465) and Muslim (782).
Following the sunnah of our Prophet Muhammad (s.a.w) also acts as a light for us on the Day of Reckoning. The more we follow the sunnah, the more light we will be provided with when we most need it, in shaa Allah.
I hope this answers your question and Allah knows best.