2Chronicles 30

Though he missed the date called for in the law, Hezekiah held the Passover as soon as he was able.

He did it right, too. Rather than just donating a lot of animals, he sent messages inviting the people of Israel to the feast. Including a rival kingdom was more than would be expected of Hezekiah, but he just thought all the Hebrews should have the same opportunity to worship.