Genesis 9:18-28

18 The sons of Noah who came out of the ark were Shem, Ham and Japheth. (Ham was the father of Canaan.) 19 These were the three sons of Noah, and from them came the people who were scattered over the earth.

20 Noah, a man of the soil, proceeded to plant a vineyard. 21 When he drank some of its wine, he became drunk and lay uncovered inside his tent. 22 Ham, the father of Canaan, saw his father's nakedness and told his two brothers outside. 23 But Shem and Japheth took a garment and laid it across their shoulders; then they walked in backward and covered their father's nakedness. Their faces were turned the other way so that they would not see their father's nakedness.

24 When Noah awoke from his wine and found out what his youngest son had done to him, 25 he said,
"Cursed be Canaan!
The lowest of slaves
will he be to his brothers."

26 He also said,
"Blessed be the LORD, the God of Shem!
May Canaan be the slave of Shem.

27 May God extend the territory of Japheth;
may Japheth live in the tents of Shem,
and may Canaan be his slave."

28 After the flood Noah lived 350 years. 29 Altogether, Noah lived 950 years, and then he died.

Now, this is obviously one of the most bizarre stories in the Bible. It makes Noah appear to be insane, and, while it doesn't explicitly endorse Noah's actions, it does make God look bad (not for the first time!) because he singled out Noah as the last righteous man and here he is behaving like a total lunatic.

Noah gets drunk and passes out naked in his tent, Ham accidentally sees him in this state and tells his brothers, and in response, Noah makes Ham's son Canaan - who apparently had nothing to do with the whole thing - the slave of his brothers.

In later years, Christians decided that Ham was the father of the Africans and used this story to justify slavery. Fortunately, I don't have to try to explain this weirdness because Cecil Adams of The Straight Dope has done it for me, in two parts, here, and here.

There are two basic points: This story comes from an earlier oral tradition, and when it got written down, something was left out, perhaps something too embarrassing for the written record such as a sex act; and the later interpretation justifying black slavery was just pure bullshit, like most interpretations of the Bible, which are made to justify foregone conclusions. As I have said many times, there are innumerable ambiguities, self-contradictions, and vague metaphors in the Bible and it's easy to decide that it means whatever you want it to mean. This may be the ultimate proof.