Iran is a Shia Muslims nation. Muslims read both the Quran and Hadiths. So what do these scriptures teach about punishment for adulteress?

Bukhari (6:60:79) - Two people guilty of "illegal intercourse" are brought to Muhammad, who commands that they both be stoned. Apparently their act was out of love, however, since the verse records the man as trying to shield the woman from the stones.

Bukhari (83:37) - Adultery is one of three justifications for killing a person, according to Muhammad.

Muslim (17:4192) - Clarifies the different penalties for adultery (when the subjects are married), and fornication (when they are not): "in case of married (persons) there is (a punishment) of one hundred lashes and then stoning (to death). And in case of unmarried persons, (the punishment) is one hundred lashes and exile for one year" (See also 17:4191)

Muslim (17:4196) - A married man confesses that he has adultery. Muhammad orders him planted in the ground and pelted with stones. According to the passage, the first several stones caused such pain that he tried to escape and was dragged back.

Muslim (17:4206) - A woman who became pregnant confesses to Muhammad that she is guilty of adultery. Muhammad allows her to have the child, then has her stoned (the description is graphic).

Muslim (17:4209) - A woman confesses adultery and is stoned to death on Muhammad's order.

Ibn Ishaq (970) - "The adulterer must be stoned." These words were a part of Muhammad's farewell address to his people on the occasion of his final pilgrimage to Mecca.