Reference for Sanhedrin 2:5

אֵין רוֹכְבִין עַל סוּסוֹ, וְאֵין יוֹשְׁבִין עַל כִּסְאוֹ, וְאֵין מִשְׁתַּמְּשִׁין בְּשַׁרְבִיטוֹ, וְאֵין רוֹאִין אוֹתוֹ כְּשֶׁהוּא מִסְתַּפֵּר וְלֹא כְשֶׁהוּא עָרֹם וְלֹא בְבֵית הַמֶּרְחָץ, שֶׁנֶּאֱמַר (שם) שׂוֹם תָּשִׂים עָלֶיךָ מֶלֶךְ, שֶׁתְּהֵא אֵימָתוֹ עָלֶיךָ:

It is not permitted to ride on his horse, to sit on his throne, to make use of his sceptre, or to see him when his hair is being cut, when he is naked, or when he is in the bathhouse, it being written (Deuteronomy 17:15): "Place shall you place over yourself a king" — his awe must be upon you.

Jastrow

Jastrow