Spreading fantasy stories about Prophets: what is the rule?

Since childhood, I had been hearing many fantasy stories about prophets and other Islamic historical persons. Some examples: * Adam (A) was 60 feet cubit tall (Its possible, but is there any evidence by Quran/Hadis reference )? * Musa (A) fought an enemy who was extremely tall (say 20 times than a normal man) * Buraq was a horse and was female. * A prophet (don't remember who) had a black Pegasus from heaven which was so beautiful that that prophet could not concentrate to his duties. As a result he cut off the Pegasus's wings. The Arabian Black horse is the children of that horse that is why Arabian Black Horse is the best quality horse (truthfulness of this last sentence is off-topic). * very descriptive conversation between Allah and Adam (A) These stories were really very nice to hear but as I grew older, I realized that most of these stories are just stories. No evidence is found either by Quran/Hadis or History. Unfortunately, I have found many matured muslims who believe many of such stories. **What does Islam say about believing or spreading such fantasy story?** I would like to warn people who do such things. *Please note that I do not claim that all those stories (including the examples here) are necessarily false. I just don't want people believe things without appropriate reference.* **Further Clarification** This question is not about lying in general. Obviously to lie is a great sin is Islam. By Fantasy story, I mean those which appears to be impossible. For example, the Miraj of Muhammad(Sm) and Musa(A) fighting a 20 times tall Man. However, the first one is obviously true (I am sure someone can quote from Quran/Hadith) while the second one may or may not because from whom I heard this did not give me a reference. The problem is: because these stories are about prophets, people usually believe them as Allah often gave prophets unusual power. I am sure a false story may become very harmful, specially when offering Islam to a non-muslim. Therefore, I would like to know what Islam says about spreading them. Or, a more general question may be equivalent to this question: **What Islam says about telling something that *may or may not* be true? And what about believing such things?**