《资治通鉴·唐纪·唐纪十九》
太后想遍知人间的事情，鱼保家便上书，请求铸铜匦以接受天下人的秘密上奏。
太后欲周知人间事，保家上书，请铸铜为匦以受天下密奏。
The Empress Dowager wished to thoroughly understand human affairs; Yu Baojia, thus, submitted a memorial, asking to cast copper ballot boxes in order to receive secret reports from people across the country.