Your description of a credible source may be different depending on your beliefs. Usually, when you are writing an academic paper, you would need to cite sources that can prove that they have some pieces of evidence about the things that they are talking about. You need to find sources that will provide details that will prove the details that have been said.
There are some credible sources that will provide even more sources for you just to show that they know what they are talking about. There is also a discussion that will be provided wherein your source will try to provide an argument on why the details that are being presented are true according to their belief and their knowledge about the situation.