Put this on your config.rb to make compass generate sprite without hash.

sprite-cache.rb

# Thanks to piouPiouM
#
# @see http://stackoverflow.com/questions/9183133/how-to-turn-off-compass-sass-cache-busting/9332472#9332472
# @link http://pioupioum.fr/developpement/compass-sprites-supprimer-cache-buster.html

# Make a copy of sprites with a name that has no uniqueness of the hash.
on_sprite_saved do |filename|
  if File.exists?(filename)
    FileUtils.cp filename, filename.gsub(%r{-s[a-z0-9]{10}\.png$}, '.png')
  end
end

# Replace in stylesheets generated references to sprites
# by their counterparts without the hash uniqueness.
on_stylesheet_saved do |filename|
  if File.exists?(filename)
    css = File.read filename
    File.open(filename, 'w+') do |f|
      f << css.gsub(%r{-s[a-z0-9]{10}\.png}, '.png')
    end
  end
end