Is it permissible to say that Shiites are children of zinā (fornication) or mut'ah (temporary marriage), and is it permissible to describe a Shiite woman as an adulteress?

A Muslim is pure of speech; he does not slander people's honor nor does he judge a person to be an illegitimate child unless he came into being through a purely illicit means, such as adultery. However, for one who came into being through a valid marriage or one that contains an element of doubt, such as "Nikah (definition) al-Mut'ah" – which scholars have unanimously agreed upon its prohibition, but it is a marriage that contains an element of contractual doubt – he is not considered an illegitimate child. In such cases, lineage is attributed to the cohabitant, and punishments are averted by doubts. Not all Shi'a women practice Mut'ah, and therefore, it is not permissible to claim that Shi'a are "children of Mut'ah" or "children of adultery" without proof, for justice is obligatory with everyone.