It’s in lots of places. In the Harryhausen filmThe Golden Voyage of Sinbad the Evil Sorceror Prince Koura (played by onetime Doctor Who Tom Baker) gets older and feebler with every spell he casts. In the "magic’ stories that Larry Niven wrote, you needed something called “mana”* to produce magic, and when it was all used up in an area, you couldn’t do magic there anymore – that’s the reason for the title of his book The Magic Goes Away, and the shared-universe anthology The Magic May Return.
*“Mana” is a term for power, magical and otherwise, in Melanesia, but not used quite the way it is in Niven’s magical universe: http://en.wikipedia.org/wiki/Mana