《新五代史·列传·杂传第三十九》
唐明宗寻求能够把康延孝的诚意送达唐庄宗的人，范延光主动请求前往，于是怀揣康延孝的蜡丸书，往西拜见唐庄宗将书呈上，并且说： 如今康延孝虽有投降的打算，但扼守杨刘的梁兵很强大，不可打他的主意。不如在马家口修筑堡垒以便联络汶阳。 
明宗求可以通延孝款于庄宗者，延光辄自请行，乃怀延孝蜡丸书，西见庄宗致之，且曰： 今延孝虽有降意，而梁兵扼杨刘者甚盛，未可图也，不如筑垒马家口以通汶阳。 
Emperor Mingzong of the Tang Dynasty was looking for someone who could deliver Kang Yanxiao's letter to Emperor Zhuangzong of the Tang Dynasty. Fan Yanguang volunteered to go, taking with him a wax letter from Kang Yanxiao. He traveled west to pay homage to Emperor Zhuangzong of the Tang Dynasty, presented him with the letter, and said, "Kang Yanxiao is thinking of surrendering, but the Southern Han army guarding Yangliu is very powerful. Do not attack him lightly. Instead, it would be more effective to build a stronghold at Majiakou to facilitate communication with Wenyuan."