《太平广记·卷二十二·神仙二十二》
玄宗后来又硬要学隐形之术，劝阻不了，就只好教他。
玄宗后又坚学隐形之术，强之不已，因而教焉。
Emperor Xuanzong later insisted on learning the technique of invisibility. Since no one could dissuade him, they had no choice but to teach him.