 because his body exists with you but they exist because of a cause other than themselves. so if it is possible that they existed eternally it is possible that they do not have a cause.
لوجود جسمه عندكم بل هما يوجدان بعلة سواهما فإذا جاز وجودهما قديما جاز أن لا يكون لهما علة.