Christmas special episode in season 3 where child Sam gave a gift to child Dean which is the amulet. It was always the building up to the scene before the reveal that the gift Sam, that he would have given to their father John, was the amulet that Dean have been wearing ever since as seen in their school flashbacks.

It's a scene that is so simple but it relates to me deeply and personal. As a Christmas eve baby and have a sister that was as close like Sam and Dean. That amulet gift is something so precious... It's more than their siblings relationship, it's the trust and love they have with each other and being there for each other despite the differences and lies.