《资治通鉴·唐纪·唐纪三十一》
春季，正月庚午，玄宗对宰相说： 朕近来于甲子日在宫中设置祭坛，为天下百姓祈求幸福，朕亲自在黄素绢上写了字放置在香案上，不一会儿飞入天空，听见空中说道： 圣寿延长。 
春，正月，庚午，上谓宰相曰： 朕比以甲子日，于宫中为坛，为百姓祈福，朕自草黄素置案上，俄飞升天，闻空中语去： 圣寿延长。 
In the spring, on the Gengwu day of the first lunar month, Emperor Xuangzong told his prime minister: I recently set up an altar in the palace on a Jizi day to pray for happiness for the people of the world. I personally wrote words on yellow silk and placed them on the incense table. Soon it flew into the sky and I heard a voice in the air saying: May the saint's life be prolonged.