Therefore he had caused Hasan to be killed by poisoning...

Therefore he had caused Hasan to be killed by poisoning, thus preparing the way for his son, Yazid. In breaking his agreement with Hasan, Mu'awiyah made it clear that he would never permit the Shi'ah of the Household of the Prophet to live in a peaceful and secure environment and continue their activity as before, and he carried into action this very intention.

It has been said that he went so far as to declare that whoever would transmit a hadith in praise of the virtues of the Household of the Prophet would have no immunity or protection concerning his life, merchandise and property. At the same time he ordered that whoever could recite a hadith in praise of the other companions or caliphs would be given sufficient reward.

As a result a noticeable number of hadiths were recorded at this time praising the companions, some of which are of doubtful authenticity. He ordered pejorative comments to be made about Ali from the pulpits of mosques throughout the lands of Islam, while he himself sought to revile Ali. This command continued to be more or less in effect until the caliphate of Umar ibn 'Abd al-'Aziz, when it was discontinued.

With the help of his agents and lieutenants, Mu'awiyah caused elite and the most outstanding among the partisans of Ali to be put to death and the heads of some of them to be carried on lances throughout different cities. The majority of Shi'ites were forced to disown and even curse Ali and to express their disdain for him. If they refused, they were put to death.

The Bleakest Days of Shi'ism The most difficult period for Shi'ism was the twenty-year rule of Mu'awiyah, during which the Shi'ites had no protection and most of them were considered as marked characters, under suspicion and hunted down by the state. Two of the leaders of Shi'ism who lived at this time, Imams Hasan and Husayn, did not possess any means whatsoever to change the negative and oppressive circumstances in which they lived.

Husayn, the third Imam of Shi'ism, had no possibility of freeing the Shi'ites from persecution in the ten years he was Imam during Mu'awiyah's caliphate, and when he rebelled during the caliphate of Yazid he was massacred along with all his aides and children. Certain people in the Sunni world explain as pardonable the arbitrary, unjust and irresponsible actions carried out at this time by Mu'awiyah and his aides and lieutenants, some of whom were like Mu'awiyah himself, among the companions.