There once was a mage with quite the potential power, but what he lacked was a student to continue his teachings. So he searched a nerby city for potential students
...
Finds three who are interested.
Put them to a test, but the slowest and least witty wins and so he takes him in.
The urchin finds a bound wizard in the dungeon he is not allowed to visit and---
Caged Mage that asks for water, that foolhardy persson gives untill the mage brakes free, but grants a small wish as a return of favour.
The favor is used to defeat the dark night that was broken free and he is so made full wizard.