John Gill Commentary 1 Kings 22:9

"Then the king of Israel called an officer, and said, Fetch quickly Micaiah the son of Imlah." — 1 Kings 22:9 (ASV)

Then the king of Israel called an officer
An eunuch, as the word is sometimes used, one of pages:

and said, hasten hither Micaiah the son of Imlah ;
who, as it seems from (1 Kings 22:26) was in prison, where perhaps Ahab had cast him for his last prophecy to him, and where he had lain ever since; and this gives a reason why he could so readily send for him, knowing where he was.