Abu Sufyan was not happy on Abu Bakr...

Abu Sufyan was not happy on Abu Bakr, becoming the Caliph, because Abu Bakr’s family was the smallest amongst the different families of Quraysh. For this reason or apparently for this reason he joined ‘Ali, but when ‘Ali turned him away from his presence he was obliged to seek the favour of ‘Umar by flattering him. After Abu Sufyan had gained ‘Umar's favour, he instigated Mughira bin Sho'ba to do away with ‘Umar.

Mughira discharged this assignment quite admirably because he instigated his slave Abu Lu'lu to kill ‘Umar. Then the blood of ‘Umar, which had been shed as a consequence of the plot of Abu Sufyan, became the cause of the Caliphate of…