[Buddha-l] Magic

[Joy Vriens]

The Buddha apparently said:

"I forbid you, O bhikkhus, 
to employ any spells or supplications, 
for they are useless, 
since the law of karma governs all things. 
He who attempts to perform miracles 
has not understood the doctrine of the Tathagata."

And a lot of cheering and shouting of Hurray could be heard from the cloud of protestant Buddhist scholars above.

Can anyone tell me in what source, when and why "the Buddha" (had to) forbid the use of magic?  

<Warning: boobytrapped question>