Conversation so far:
When did Niki Lauda first retire?
In late September, during practice for the 1979 Canadian Grand Prix, Niki Lauda cut short a practice session and promptly informed team principal Ecclestone, that he wished to retire immediately.

Question: Which series of races or tournament was he competing when this happened?
Self-contained rewrite: What series of races or tournaments was Niki Lauda competing in when he announced his desire to retire?