“Do not buy fish in the sea, for it is gharar .”
–Islamic Hadith
Gharar means “speculative and risky.” This hadith, a saying of Muhammed, suggests waiting until the fish are actually caught before plopping down good money. In other words, avoid transactions in which the financial commitments become too distant from the underlying goods.
Sort of sounds like Muhammed was against sub-prime mortgages and deriviatives.