Are you trying to match

  Tue Sep  5 10:26:44 GMT 2005
[download]

If this is so, then a more appropriate regexp might be:

  /(      # start selection
    \w{3} # Tue
    \s    # one space
    \w{3} # Sep
    \s+   # one or more spaces
    \d+   # 5 (day, one or more digits)
    \s    # one space
    \d+:\d+:\d+ # 10:26:44
    \s+   # one or more spaces
    (?:\w+\s+)? # optional timezone GMT
    \d+   # year
   )      # end of selection
  /x      # x - allows whitespace in regexp
[download]

Or as a one liner:

  /(\w{3}\s\w{3}\s+\d+\s\d+:\d+:\d+\s+(?:\w+\s+)?\d+)/
[download]