Monastic Training( Eberron Campaign Setting, p. 57)
You are part of an order that combines the monastic discipline of the monk class with another form of training.
Tashalatora (SoS) ,
Pick one class. Taking levels in this class does not prevent you from taking monk levels. If you take levels in any other class, you lose your ability to progress as a monk as usual. If the selected class also has restricted advancement, such as the paladin class, taking monk levels does not prevent you from advancing in that class.
A monk can take this feat as his bonus feat at 1st, 2nd, or 6th level.