וּבִשְׁנַ֣ת עֶשְׂרִ֔ים לְיָרָבְעָ֖ם מֶ֣לֶךְ יִשְׂרָאֵ֑ל מָלַ֥ךְ אָסָ֖א מֶ֥לֶךְ יְהוּדָֽה׃
И в двадцатый год Иеровоама, царя Израильского, начал царствовать Аса над Иудеей.
Rashi
Three years he reigned in Jerusalem and no more, as is proven in I Kings (15:9): “And in the twentieth year of Jeroboam, king of Israel, Asa reigned over Judah.” We find that he did not reign even three whole years.