Righteous Calling (3.5e Feat)
From D&D Wiki
Righteous Calling [General]
The call to arms in a righteous cause can overpower preconceived notions of a person's destiny
Benefit: The character gains Paladin as a favoured class & may multiclass freely to & from it without penalty.
Normal: A character's favoured class is decided by race & a Paladin who persues a different class can never again return to the ways of the Paladin.