Ezekiel 43:12-13

This is the law of the house: upon the top of the mountain the whole limit thereof round about shall be most holy. Behold, this is the law of the house. And these are the measures of the altar by cubits (the cubit is a cubit and a handbreadth): the bottom shall be a cubit, and the breadth a cubit, and the border thereof by the edge thereof round about a span; and this shall be the base of the altar.