Is it considered disbelief to state incorrect information about the religion, such as prohibiting what is permissible, out of assumption and not intention, and then not correcting it to those to whom it was said, knowing that this information might be considered an act of disbelief?

It is not permissible to rule something lawful or unlawful without knowledge, because speaking about Allah without knowledge is one of the gravest sins. Whoever issues a fatwa without knowledge must repent to Allah and strive to correct his error. One who issues a fatwa without knowledge does not commit an act of disbelief unless he believes in the unlawfulness of what is lawful or the lawfulness of what is unlawful according to the Sharia. Excommunication (takfir) is a serious matter, and a person is not excommunicated except after all conditions are met and all impediments are removed. Whoever obeys someone in a religion not authorized by Allah has incurred blame.