Historical Rules · 18 June 2010
Rule 603.2c
Official source text from the 18 June 2010 Rules release
An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains multiple occurrences. See also rule 509.4. 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.