《论衡·卷十七·指瑞篇》
白鱼、赤乌是小瑞物，是小安的征兆；凤凰、麒麟是大瑞物，是天下太平的征兆。
若夫白鱼、赤乌小物，小安之兆也；凤皇、骐驎大物，太平之象也。
In the category of auspicious omens, the white fish and red crow are small omens, and they are signs of minor good fortune; the phoenix and qilin are great omens, and they are signs of peace and prosperity throughout the world.