What is the ruling on saying something bad about marriage—such as “لع”—to someone who does not realize that marriage is part of the religion?

If a person is unaware that marriage is part of religion and does not intend to disparage what Allah has legislated, then he does not commit an act of disbelief (kufr) by that, because he is not knowledgeable, intentional, and volitional. However, he does sin by cursing what does not deserve to be cursed.