וְלֹֽא־עָצַ֧ר כֹּֽחַ־יָרָבְעָ֛ם ע֖וֹד בִּימֵ֣י אֲבִיָּ֑הוּ וַיִּגְּפֵ֥הוּ יְהוָ֖ה וַיָּמֹֽת׃ (פ)
Auch Jerobeam erholte sich in den Tagen Abijas nicht wieder; und der HERR schlug ihn und er starb.
Rashi on II Chronicles
And Jeroboam could muster no more strength, etc., and the Lord smote him i.e., Jeroboam.
Rashi on II Chronicles
and he died He did not die immediately, but continuously deteriorated because of the wars, and in Genesis Rabbah (65:20), it is explained that the Lord smote Abijah.