John Gill Commentary Genesis 9:23

"And Shem and Japheth took a garment, and laid it upon both their shoulders, and went backward, and covered the nakedness of their father. And their faces were backward, and they saw not their father`s nakedness." — Genesis 9:23 (ASV)

And Shem and Japheth took a garment
Who were the two brothers Ham told what he had seen, and who, no doubt, reproved him for his ill behaviour, and then took a garment, a coat of their own, very probably, some large garment fit for the purpose;

and laid it upon both their shoulders ;
one part of it on the right shoulder of the one, and the other on the left shoulder of the other:

and went backward, and covered the nakedness of their father ;
going backward when they came into the tent, and to the place where their father lay, they threw the garment off from their shoulders over him, and so covered him:

and their faces were backward, and they saw not their father's
nakedness :
which they purposely shunned, for which reason they went backwards, and their faces were backwards to their father; which showed their modesty, and their filial piety and duty, and thus by their actions reproved Ham, as well as doubtless they did by words.