Genesis 4:20 (KJV)

And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.

And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden.

And Cain knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch.

And unto Enoch was born Irad: and Irad begat Mehujael: and Mehujael begat Methusael: and Methusael begat Lamech.

And Lamech took unto him two wives: the name of the one was Adah, and the name of the other Zillah.

And his brother's name was Jubal: he was the father of all such as handle the harp and organ.

And Zillah, she also bare Tubalcain, an instructer of every artificer in brass and iron: and the sister of Tubalcain was Naamah.

And Lamech said unto his wives, Adah and Zillah, Hear my voice; ye wives of Lamech, hearken unto my speech: for I have slain a man to my wounding, and a young man to my hurt.

If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold.

And Adam knew his wife again; and she bare a son, and called his name Seth: For God, said she, hath appointed me another seed instead of Abel, whom Cain slew.