During one of the wars between the English and French, two war vessels met in fearful encounter. It was too dark to distinguish friends from foes; but each supposed itself engaged with the common enemy. When the darkness lifted, both ships were seen flying the English flag. They saluted each other, and grieved sadly over their disastrous mistake.
Source: “Strife Among Christians Often the Result of Mistake,” BibleHub: Phil. 4:2 as shared by Richard Tow in his sermon entitled "Standing Firm in Difficult Times."