笑比河清的英文是「to make one smile is as difficult as to purify the river」
xiao bi he qing
形容态度严肃,难见笑容。
《宋史·包拯传》:“立朝刚毅,贵戚宦官为之敛手,闻者皆惮之。人以包拯笑比黄河清。”