To be fair, the prayer was in Italian, not Francis's native Spanish, and the Italian word for "Fuck" ("cazzo") is close to the Italian word "caso" ("example" or "case"), which is what the Pope was trying to say. He quickly corrected his mistake.
Aside from the accidental "fuck," it seemed like a very nice blessing.
"If each one of us does not amass riches only for oneself, but half for the service of others, in this fuck [pause], in this case the providence of God will become visible through this gesture of solidarity," Francis told followers gathered in St Peter's Square, according to the Local.
UPDATE: As some commenters have pointed out, "cazzo" technically translates to something like "dick" or "cock," though Italians most often use it to mean "fuck" (Google Translate also defines it as "fuck"). So, for the sake of accuracy: Pope Francis either said "fuck" or "cock" during his weekly blessing on Sunday.