Historical Rules · 5 October 2018
Rule 605.1b
Official source text from the 5 October 2018 Rules release
A triggered ability is a mana ability if it meets all of the following criteria: it doesn’t have a target, it triggers from the resolution of an activated mana ability (see rule 106.11a) or from mana being added to a player’s mana pool, and it could add mana to a player’s mana pool when it resolves.