Genesis 9:20-23

And Noah began to farm and cultivate the ground and he planted a vineyard. He drank some of the wine and became drunk, and he was uncovered and lay exposed inside his tent. Ham, the father of Canaan, saw [by accident] the nakedness of his father, and [to his father’s shame] told his two brothers outside. So Shem and Japheth took a robe and put it on both their shoulders, and walked backwards and covered the nakedness of their father; their faces were turned away so that they did not see their father’s nakedness.