That's Noah and his sons (after the flood), when Noah got drunk and passed out and his son(s) saw him passed out and naked. I don't believe they (he?) sexually assaulted his/their father (Noah). The Old Testament sin, as I understand it, was seeing one's father, the patriarchal elder, in a disrespectful/embarrassing way, even though it was Noah's fault he was drunk, passed out and naked.