Context of 53:3-4 is quite clearly referring to Quran alone:
53:1 Witness are the Stars that set along a course appointed. [They never misguide you. He Who commands them, commands the Messenger 6:98, 56:75. Wa = And = Consider = Witness = For = By. Najm is singular as well as plural in the form of a galaxy]
53:2 Your honored companion is neither in error, nor is he misled.
53:3 Nor does he utter the Word out of his desire.
53:4 This (Qur’an) is but a revelation that is being revealed to him.
53:5 He has been taught by the One Mighty in Powers.
53:6 The Owner of authority and wisdom established him (the Prophet).
53:7 At the highest horizon, [81:23]
53:8 Of human wisdom and knowledge as he drew near and approached (the point where the human intellect comes to a halt),
53:9 Till he was but two bow-lengths away, or even closer. [The Divine will and the will of the Messenger merged together, like the two of you join your bows as a token of friendship. 8:17]
53:10 And thus He revealed to His servant what He revealed.
53:11 And never did he find contrary to reason what he learned. [2:285, 6:164. Raa = Saw, learned, observed, took to heart]
53:12 Will you, then, contend with him concerning what he has learned (that you have not)?
53:13 He has recalled the revelation (on his heart) once again. [2:185]
Every single reference to revelation in the Quran is directing us to the Quran but some think differently:
38:1 S. Saad. (The Saadiq, Truthful God states that), This Qur’an stands witness (with internal evidence) that it is a profound Reminder worth taking to heart and it can give you eminence. [21:24, 23:70, 43:43-44]
38:2 Nay, but those who disbelieve have plunged into arrogance and thus into opposition. [Shiqaaq = Opposition, schism, splitting. If they reflect on the Qur’an in all humility, they will accept the Divine truth rather than opposing it]
The verse you quoted about Salat of Abraham is again devoid of any physical ritual to be performed and Dr Shabbir has correctly rendered this as:
2:125 Remember, We appointed the House (Ka’bah) a means to achieve unity among all mankind, and thus, a source of peace and security. So, attain the stature of Abraham recalling his firm stand (for Monotheism) and closely follow the Divine Commands. We did take a Covenant from Abraham and Ishmael, “Keep My House clean of all falsehood for those who rally around it and those who strive hard for the noble objectives, and for those who submit in humility to the Divine Commands."
Believe in One God and everything, including the shadows follow the commands of God. You dismissed the birds, now dismiss the shadows, everything living or none living, and good luck putting salat = physical ritual, sujood = physical prostration, so words have be altered for the Quran but the Quran fights back :
13:14 Calling upon Him is the True calling. Those unto whom they call besides God, cannot respond to them at all. Thus, they are like the one who stretches forth his two palms towards water hoping for it to reach his mouth from distance, and it will never reach. Likewise, the calling of those who are oblivious to Divine laws is misdirected. [4:123]
13:15 And before God bow, willingly or unwillingly, all beings that are in the heavens and earth, as do their shadows in the mornings and evenings. [3:82, 41:11]
16:48 Have they not observed the things that God has created? Their shadows incline to the right and to the left; that is their utter submission to God, in all humility. [Even the shadows can show you that the entire Cosmos, with its celestial bodies, is submitting to His laws]
16:49 Indeed, before God, bows in submission all that is in the heavens and all that is on earth, whether living beings or the angels, for none are arrogant. ['All that is' includes three classes of God’s creation: Inanimate things, living beings, and angels. Angels, here, represent God’s forces in nature]
24:41 Do you not realize that God, He is the One Whom all beings in the heavens and earth glorify, and the birds, with their wings outspread, as they fly in columns. All of them know their Salaat and Tasbeeh (mission and strife). God is Aware of what they do to fulfill His Plan.
[All creatures know their Salaat, their inborn Divinely programmed instincts. So, they can automatically strive (do their Tasbeeh) in the best way. But humans are not programmed with such inborn instincts. Given free will, they must do their Salaat by following the revealed guidance and thus strive (do Tasbeeh) in the best way]