White Stone of Legend's effect will activate when he is sent to the graveyard no matter where he was sent from. You can tribute him on your field, have your opponent destroy him, discard from your hand, mill from your deck, return from banish zone to graveyard, etc. will all trigger his search effect.
Blue-Eyes White Dragon
You can search out Blue-Eyes White Dragon when White Stone of Legend is sent to the graveyard. You can Synchro Summon Azure-Eyes Silver Dragon with White Stone of Legend and a level 8 Normal monster, like Blue-Eyes White Dragon, as materials.