xiōng dì xì yú qiáng, wài yù qí wǔ 兄弟阋于墙，外御其侮
Brothers Quarrel within the Walls of the Home; Outside They Resist Bullying by Others.
Although brothers may quarrel at home, they always stick together to resist bullying by outsiders. This refers to people who have internal conflicts and disputes can still put together to resist aggression. It gives full expression to the desire of the Chinese people to stick together in time of crisis. In modern times, this expression has been used to symbolize the unity of Chinese nation when facing a survival crisis caused by foreign aggression.
Fu Chen remonstrated: “This is not permissible. There is a saying by the ancients:’Brothers may quarrel with each other, but they can still keep those who want to bully them at a distance of a hundred li.’ The Duke of Zhou said in a poem:’Brothers quarrel within the walls of their home; outside they resist bullying by others.’ Thus, a quarrel between brothers is an internal dispute, and such quarrel will not weaken their family bond.” (Discourses on Governance of the States)