phrase/le.z‿a.fɛʁ sɔ̃ le.z‿a.fɛʁ/
business is business
“[…]en disant toujours qu'il ne se méfiait pas de son gendre, mais en répétant ce vieux proverbe des négocians: Les affaires sont les affaires.” — […] always saying that he did not mistrust his son, yet repeating the old mercantile proverb: Business is business.
Possibly a calque of English business is business (or vice versa). Perhaps popularized by the title of Octave Mirbeau's 1903 play Les affaires sont les affaires, although the phrase had already been used in the mid-19th century by George Sand and Eugène Sue, among others.