en_tn/1ki/16/12.md

the word of Yahweh

"the message of Yahweh" or "Yahweh's message"

which he spoke against Baasha by Jehu the prophet

Speaking "by" a prophet represents telling a prophet to speak and the prophet speaking. Alternate translation: "that Yahweh told Jehu the prophet to speak against Baasha" (See: rc://en/ta/man/jit/figs-idiom)