This Bible contradiction is from the Skeptic's Annotated Bible.
Abijam was Asa's father.
1 Kings 15:8 View context
And Abijam slept with his fathers; and they buried him in the city of David: and Asa his son reigned in his stead.
Abijam was Asa's brother. (They both had the same mother, Maachah.)
1 Kings 15:1-2 View context
Now in the eighteenth year of king Jeroboam the son of Nebat reigned Abijam over Judah.
Three years reigned he in Jerusalem. And his mother's name [was] Maachah, the daughter of Abishalom.