How do you spell "from behind"?

With the spelling of the word "from behind"some problems. First - is it separate or combined to write: "behind" or "from behind"? The correct option is the first one. Since this word is an adverb, it can not be torn from the prefix "c". The word "Zadi" does not exist. Also, some are interested in how it is written "from behind": through the letter "з" or "с". Correctly to write "behind", since the prefix "з" does not exist in Russian. So, the right version of writing: back.