The Unwavering Path (2006)

A Multiclassing Quest for Monks and Paladins
Levels 3-5

From the website:

The Players Handbook II (D&D 3.5e) introduces the idea of rebuild quests for when players want to alter their characters more extensively than retraining can accommodate. The multiclassing quest of this article is somewhat different in that it deals specifically with granting characters the ability to multiclass "back into" the monk or paladin class after taking levels in classes or prestige classes that do not normally permit a monk or paladin to freely multiclass.

From PDF Introduction

Monks and paladins, lawful professions at heart, demand consistency of themselves more than any other quality. Both classes adhere to traditions for the sake of creating standards upon which they can always count. From the repetition of exercise, meditation, and prayer, both classes reinforce the strength of their convictions, whether from within (the self) or from
without (the divine). As such, the moment their focus changes to pursue a different path, for even one level, both classes must forever abandon that profession. These characters must make a lasting choice before multiclassing, deciding if they have advanced far enough as monks or paladins for their entire career.