Is it a sin to laugh in Islam?

I noticed some elders laughing yesterday after which they said astughfirullah, I mustn't laugh.

Why did they say that? Does Islam not allow you to laugh?

As they were laughing, they said, astugfirullah, we shouldn't be laughing, calamity will befall on us.

They were laughing at the funny sound those ear pieces make which people were who need help with their hearing.

Just to clear up, 1 of the elders laughing was the 1 wearing the hearing aid, and was laughing because it was making a funny sound apparently.

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