Genesis 4:23

a man for wounding me Lamech boasts that he has slain a man who had wounded him and a young man who had bruised him. Whether "a man" and "a young man" are the same person, or whether they mean a man and his son, cannot be decided. Lamech has exacted the vengeance of death for the insult of a blow 2 [11].

[11] See for an explanation by Jewish tradition Appendix B.

It is, however, possible that the poem only describes an imaginary instance in which Lamech had retaliated in self-defence, and boasts that with the assistance of metal weapons Lamech's capacity for revenge is increased elevenfold.