What is the Three Musketeers' motto?

"All for one, one for all" is a motto traditionally associated with the titular heroes of the novel "The Three Musketeers" written by Alexandre Dumas père, first published in 1844. In the novel, it was the motto of a group of French musketeers named Athos, Porthos, Aramis, and D'Artagnan who stayed loyal to each other through thick and thin.

Source: Wikipedia