Rashi on Exodus 25:20/רש"י על שמות כ״ה:כ׳

1פרשי כנפים [AND THE CHERUBIM SHALL] SPREAD THEIR WINGS [ON HIGH] — i. e. that you shall not make their wings touching the body but spreading on high slightly above but almost on the same level with their heads so that the hollow space between the wings and the cover shall be ten handbreadths, as it is explained in Treatise Sukkah 5b.