Also seit 3E gilt das eigentlich nicht mehr. Seit 4E ist der Verhaltenskodex auch nicht mehr restriktiv. 
Aus dem  3e PHB (p.43):
"Ex-Paladins
A paladin  who  ceases  to  be  lawful  good,  who  willfully  commits  an evil  act,  or  who  grossly violates the code of conduct loses all special abilities  and  spells,  including  the  service  of  the  paladin’s  warhorse. She  also  may  not  progress  in  levels  as  a  paladin.  She  regains  her abilities  if  she  atones  for  her  violations  (see  the atonement  spell description, page 176), as appropriate."
Aus dem 3.5 PHB (p. 44-45):
"Ex-Paladins 
A  paladin  who  ceases  to  be  lawful  good,  who  willfully  commits  an  evil act, or who grossly violates the code of conduct loses all paladin spells and abilities (including the service of the paladin’s mount, but not  weapon,  armor,  and  shield  proficiencies).  She  may  not  progress any  farther  in  levels  as  a  paladin.  She  regains  her  abilities  and  advancement  potential  if  she  atones  for  her  violations  (see  the  atonement spell description, page 201), as appropriate. Like  a  member  of  any  other  class,  a  paladin  may  be  a  multiclass  character, but multiclass paladins face a special restriction. A paladin who  gains  a  level  in  any  class  other  than  paladin  may  never  again  raise  her  paladin  level,  though  she  retains  all  her  paladin  abilities.  The  path  of  the  paladin  requires  a  constant  heart.  If  a  character  adopts  this  class,  she  must  pursue  it  to  the  exclusion  of  all  other  careers. Once she has turned off the path, she may never return."
Aus dem 4e PHB (p.90), markiert von mir:
"Paladins and Deities
As fervent crusaders in their chosen cause, paladins must choose a deity. Paladins choose a specific faith to serve, as well as an alignment. You must choose an alignment identical to the alignment of your patron deity; a paladin of a good deity must be good, a paladin of a lawful good deity must be lawful good, and a paladin of an unaligned deity must be unaligned. Evil and chaotic evil paladins do exist in the world, but they are almost always villains, not player characters. [...] 
Once initiated, the paladin is a paladin forev-ermore. How justly, honorably, or compassionately the paladin wields those powers from that day forward is up to him, and paladins who stray too far from the tenets of their faith are punished by other members of the faithful."
Für die 5e zitiere ich mal aus DNDBeyond:
"Breaking your oath
[...] If a paladin willfully violates his or her oath and shows no sign of repentance, the consequences can be more serious. At the DM’s discretion, an impenitent paladin might be forced to abandon this class and adopt another, or perhaps to take the Oathbreaker paladin option that appears in the Dungeon Master’s Guide."
Die 4e ist hier also klarer Ausreißer und alle anderen Editionen erlegen dem Paladin einen Verhaltenskodex auf, dessen Bruch dazu führen kann, dass der Paladin kein Paladin mehr ist.
Oder hast du da andere Belegstellen im Kopf?