John Gill Commentary 2 Kings 10:20

"And Jehu said, Sanctify a solemn assembly for Baal. And they proclaimed it." — 2 Kings 10:20 (ASV)

And Jehu said, proclaim a solemn assembly for Baal
Such as with the Jews was a holy convocation, when they were forbidden and restrained from doing any work on that day; and such a day Jehu would have appointed and proclaimed for Baal, that the people might be at leisure to attend.

and they proclaimed it
according to his order, in Samaria.