According to several sources this took place on the 25th of November, 2013 in the area of East Ghouta, Damascus. The FSA accused them of being Hezbollah fighters. Apparently, they also were tortured before they were beheaded.
LiveLeak (h/t golem bar) One source said that the executors were the terrorist organization Jabhat al-Nusra, the other one said it was the Islamic State in Iraq and Levante. Either way, both are terrorist groups now embedded with the U.S.-funded FSA ‘rebels.’ The message of the original uploader is to behead all their enemies and to send the heads as gifts to their families.