Historical Rules · 1 October 2009
Rule 603.7d
Official source text from the 1 October 2009 Rules release
The source of a delayed triggered ability created by a spell is that spell. The source of a delayed triggered ability created by another ability is the same as the source of that other ability. The controller of a delayed triggered ability is the same as the controller of the spell or ability that created it, even if that player no longer controls its source.