Virtues and Merits of the Prophet (pbuh) and his Companions

Bukhari :: Book 4 :: Volume 56 :: Hadith 666

Narrated Ibn Abbas:

I heard 'Umar saying, "May Allah Curse so-and-so! Doesn't he know that the Prophet said, 'May Allah curse the Jews for, though they were forbidden (to eat) fat, they liquefied it and sold it. "