Vouloir faire passer un chameau par le chas d'une aiguille

Literally: To try to pass a camel through the eye of a needle

Example: “Caser tous ces meubles dans la camionnette, c'est vouloir faire passer un chameau par le chas d'une aiguille.” — Squeezing all this furniture into the van is attempting the impossible.

Origin: From the Gospels, where it is easier for a camel to pass through the eye of a needle than for a rich man to enter the kingdom of God. A persistent theory that 'needle's eye' was a narrow Jerusalem gate has no archaeological support — the absurdity is the point.