Who killed Jeroboam's sick son?

God

At that time Abijah the son of Jeroboam fell sick. ...

And the LORD said unto Ahijah, Behold, the wife of Jeroboam cometh to ask a t hing of thee for her son; for he is sick: thus and thus shalt thou say unto her: ...

Arise thou therefore, get thee to thine own house: and when thy feet enter into the city, the child shall die. ...

And Jeroboam's wife arose, and departed, and came to Tirzah: and when she came to the threshold of the door, the child died. 1 Kings 14:1-17