A number of them met in Mecca and discussed the 659 Battle of Nahrawan, which took place as a consequence of Siffin, wherein most of their men were eradicated while facing Ali's army. They concocted a plot to assassinate three prominent Muslim personalities: Amr ibn Bakr al-Tamimi was to kill 'Amr ibn al-'As, al-Hujjaj al-Tamimi was to kill Mu'awiya ibn Abu Sufyan and ibn Muljam was tasked to kill the caliph, Ali.
A group of individuals met in Mecca and discussed the Battle of Nahrawan, which followed the Siffin conflict. During this battle, many of their men were killed while fighting against Ali's army. They then planned a plot to assassinate three prominent Muslim leaders: Amr ibn Bakr al-Tamimi was tasked with killing 'Amr ibn al-'As, al-Hujjaj al-Tamimi was assigned to kill Mu'awiya ibn Abu Sufyan and ibn Muljam was ordered to eliminate the caliph, Ali.