In Iran, Mother's Day is celebrated on 20 Jumada al-thani. This is the sixth month in the Islamic calendar (a lunar calendar) and every year the holiday falls on a different day of the Gregorian calendar. This is the birthday anniversary of Fatimah, Prophet Muhammad's only daughter according to Shia Islam. On this day, banners reading ""Ya Fatemeah" (O! Fatemeh)" are displayed on "government buildings, private buildings, public streets and car windows." Mother's Day was originally observed on 16 December but the date was changed after the Iranian Revolution in 1979. The celebration is both Women's Day (replacing International Women's Day) and Mother's Day.