Also, the above statement makes no sense & is invalid to justify ISIS' attempted genocide of Yazidis.
Yazid 1 per above quote from the BBC article/link, was a Sunni & 2nd Caliph after Mohmmad's death in Sunni tradition. He beheaded Hussein (the 3rd Shia imam) who was Mohammad's grandson, son of Ali ibn talib the 1st Shia imam.
Shi'ites in Iran & Arab world revere Hussein, especially during Ashura mournings. So, it makes no sense for ISIS, who are essentially Sunni (ok, mostly Salafi but still Sunni), to hate Yazid & therefore Yazidis, even if there were a link between the two!
True enough.