If I am not mistaken there has been a previous ruling (in reference to Beorn hero) that a card ability is in effect only as long as the card is in play, and while cards are in the discard pile abilities no longer works (except for cards like Elven-Light or ally Glorfindel which specifically says differently of course). I am having a little trouble finding it, so I wanted to ask if someone could help me with that.

Most of what you are looking must be in the core set rule book or the rules reference. So there is not even need to fetch for an official answer. The following quotes are from the web rule reference.

Out of play areas are anything outside the game hands, decks and discards pile. All the rest seem to be in play areas.

The precision that must concern Beorn is:

Quote

Card abilities can only be initiated or affect the
game from an in-play area unless they specifically
refer to being used from an out-of-play area, or
require that the card be out of play for the ability
to resolve. Play restrictions and permissions are an
exception that may affect how a card may or may
not be deployed or used.

I also found, about in play :

Quote

Constant Ability
A constant ability is any non-keyword ability whose
text contains no boldface timing trigger defining its
ability type. A constant ability becomes active as soon
as its card enters play and remains active while the card
is in play.

and

Quote

Only cards in play have their ability.

Card abilities only interact with, and can only
target, cards that are in play, unless the ability
specifically refers to an out-of-play area or element.
Card abilities on characters and attachments can
only be initiated or affect the game from an inplay
area unless they specifically refer to being
used from an out-of-play area, or require that the
card be out of play for the ability to resolve. Event
cards implicitly interact with the game from an
out-of-play area, as established by the rules of the
event cardtype.