He knows he'll meet his 72 houris soon and he wants to make sure his mom will reincarnate in time as one of them 

IS man executes own mother in public for asking to leave group

By AT Editor on January 8, 2016in Asia Times News & Features, Middle East   (From Independent)

In a shocking incident, an Islamic State (IS) militant publicly executed his own mother after accusing her of apostasy, according to a rights group.

Ali Saqr al-Qasem shot his mother Lena in the head with an assault rifle

Raqqa is Being Slaughtered Silently (RIBSS) said 20-year-old jihadi Ali Saqr al-Qasem shot his mother Lena, 45, in the head with an assault rifle in front of a large crowd.

Lena al-Qasem is understood to have been accused of apostasy – a crime that usually means leaving one’s religion but in practise is used by IS as a justification for murdering anybody who does not support or speaks out against the terror group. The exact charge against al-Qasem was “inciting her son to leave the Islamic State and escaping together to the outside of Raqqa”, according to the Syrian Observatory of Human Rights. Read More

http://atimes.com/2016/01/is-man-executes-own-mother-in-public-for-asking-to-leave-group/