The saying 'brothers may quarrel at home, but they stand together against insults from outside' comes from 'The Bush Cherry'.
Tips
culture
The ode opens with the bush cherry in flower and then states its theme: 凡今之人,莫如兄弟。 'Of all people now, none are as close as brothers.' Its line 脊令在原 'wagtails on the plain' made the wagtail, 鹡鸰, a byword for brothers who rush to help each other.
usage
Often written 棠棣, and in literary writing both names stand for brothers.