Historical Rules · 25 January 2019
Rule 605.1b
Official source text from the 25 January 2019 Rules release
A triggered ability is a mana ability if it meets all of the following criteria: it doesn't require a target (see rule 114.6), 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.