[Just to let you know, the text below is a transcription of what I've said in this video. So please excuse any words or phrases that don't quite look right.]
<< وَلِلَّهِ يَسجُدُ مَن فِي السَّماواتِ وَالأَرضِ طَوعًا وَكَرهًا وَظِلالُهُم بِالغُدُوِّ وَالآصالِ ۩ >>
wa-li-llāhi yasjudu man fī s-samāwāti wa-l-ʾarḍi ṭawʿan wa-karhan wa-ẓilāluhum bi-l-ghuduwwi wa-l-ʾāṣāli
To Allah prostrates whoever there is in the heavens and the earth, willingly or unwillingly, and their shadows at sunrise and sunset. [Qur’an, 13:15]
None of the verses here contain the word Salat. However, for context, it's important to look at all of the verses where the word Salat or derivative is explicitly mentioned, as well as verses where the three core components of Salat are also mentioned.
What are the three core components? Standing (when Allah talks about standing to pray), bowing (the Ruku') and prostration (Sujood).
Sometimes these components are mentioned in certain verses without explicitly mentioning Salat. But standing, bowing, and prostrating are all part of prayer, so we'll look at these too.
In this particular verse, Allah is mentioning the Sajdah:
<< وَلِلَّهِ يَسجُدُ >>
That everything prostrates or submits.
Everything, the heavens and the earth, to God alone.
<< طَوعًا وَكَرهًا >>
Willingly or unwillingly.
<< وَظِلالُهُم بِالغُدُوِّ وَالآصالِ >>
wa-ẓilāluhum bi-l-ghuduwwi wa-l-ʾāṣāl
As do their shadows in the mornings and in the evenings.
Just as their shadows automatically follow and submit to a certain order, everything out there is prostrating, is submitting. Some do it willingly, some do it unwillingly.
What does this mean?
It means even those who deny God are submitted to Him. Are bound by Him. There is an extent to which they are prostrate, even though they're not physically prostrate.
You can't escape Allah. You can't remove yourself from His purview. Not from His vision, His knowledge or His will. So where are you going?
As Allah says [Qur’an, 81:26]:
<< فَأَينَ تَذهَبونَ >>
Where are you going?
Why don't you just align yourself? Why don't you just get on track? Get on the straight path. Go fast forward. Accelerate towards your Lord.
Allah says [Qur’an, 51:50]:
<< فَفِرّوا إِلَى اللَّهِ >>
fa-firrū ʾilā llāhi
So flee towards your Lord.
Because everything out there, everything out there prostrates and submits to Him.