603.2c An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains multiple occurrences. Example: A permanent has an ability whose trigger condition reads, “Whenever a land is put into a graveyard from the battlefield, . . . .” If someone casts a spell that destroys all lands, the ability will trigger once for each land put into the graveyard during the spell’s resolution.
Commander/EDH Decks:
BRG The Blood of Jund - Kresh the Bloodbraided BRG
WR The Blades of Goldnight - Gisela, Blade of Goldnight WR
Example: A permanent has an ability whose trigger condition reads, “Whenever a land is put into a graveyard from the battlefield, . . . .” If someone casts a spell that destroys all lands, the ability will trigger once for each land put into the graveyard during the spell’s resolution.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules