Okay, so imagine you have a book that tells you stories about a really cool person who lived a long, long time ago. These stories are supposed to teach you how to be a good person too.
But some people say that not all the stories in that book are true. They think that maybe some of the stories were made up or changed over time by people who wanted to make the cool person look even cooler or to fit their own ideas.
These people are called critics of hadith. Hadith are stories about Prophet Muhammad (peace be upon him) and his companions that have been handed down through history from people who were there when the stories happened.
Critics of hadith believe that it's important to check if the stories are true. They use special tools to figure out if the hadith is really something that the Prophet Muhammad (peace be upon him) said or did. These tools include checking the chain of people who passed down the story to make sure they were reliable, studying the language and culture of the time to see if the story makes sense, and comparing the story to other stories to make sure it doesn't contradict what we know about the Prophet Muhammad (peace be upon him).
By doing this, they hope to make sure that people are only learning the true stories of the Prophet Muhammad (peace be upon him) and not something made up or changed over time.