Exodus 36:28 Midrash

וּשְׁנֵ֤י קְרָשִׁים֙ עָשָׂ֔ה לִמְקֻצְעֹ֖ת הַמִּשְׁכָּ֑ן בַּיַּרְכָתָֽיִם׃

And two boards made he for the corners of the tabernacle in the hinder part;