Is Space Complexity Always Less Than Or Equal To Time Complexity?
The reason it's common knowledge and not formally proved anywhere is because it's obvious.
During each time step, you can only access one memory location. Therefore you can never access more memory locations than you have time.

I found the following reference, showing an even slightly stronger result: every deterministic multitape Turing machine of time complexity $t(n)$ can be simulated by a deterministic Turing machine of tape complexity $t(n)/\log t(n)$.


  If it is true that space complexity is always less than or equal to time complexity, then instead of doing a logspace reduction, I can show that the reduction can be done in log time, which is much easier in my particular case.


This suggests that something is wrong with your understanding. Showing that it runs in logarithmic time is strictly harder than showing it uses logarithmic space. Something really weird has happened. As Robert Anderws rightfully points out in his comment, no reduction from the Circuit Value Problem can run in logarithmic time and be correct, since it can't even read the entire input.