Qur'an 16:116

But say not - for any false thing that your tongues may put forth,- "This is lawful, and this is forbidden," so as to ascribe false things to Allah. For those who ascribe false things to Allah, will never prosper.

I found this verse to be very important because the verse before this one 16:115, was describing the conditions of what food is permissible and what is not allowed.  This is a clear and open warning for Muslims not to forge lies against Allah, by telling people something is disallowed in contradiction to the Qur'an.

Some common examples may be that many Muslims believe crab and lobster is haram, even though all the Qur'an speaks of is that seafood is lawful for us, yet at some point in history people began to add to the list of haram foods, out of their own desires, in contradiction to the Qur'an.

This is a clear example of many fallacies that have been introduced by Muslims, and the legacy that continues based on the lack of knowledge of people simply believing what their parents or Imams tell them.  Insha'Allah, the truth of the Qur'an will spread so people will be more knowledgeable.