Yazeed Ibn Mu`awiyah is not a sahabi (companion of the Prophet (peace and blessings be upon him)), because he was born during the caliphate of `Uthman Ibn `Affan. Ali Ibn Abu Talib was killed in 40 AH., whereas Yazeed was appointed to be a caliph after his father’s death in 60 AH. So, Yazeed was not in authority during the wars with Ali Ibn Abu Tablib, May Allah be pleased with all the companions of the Prophet (peace and blessings be upon him).