Probably from the film Apollo 13, which depicts (likely wise) hesitance to fire the SPS due to suspected damage and instead firing midcourse correction burns with the LEM descent stage while attached to the CSM. By contrast, during the otherwise normal Apollo 11, SPS was responsible for returning Collins and the CSM to Earth (TEI) whether he retrieved Armstrong and Aldrin or not. The latter case was a rehearsed abort and the stakes were known, but the maneuver was otherwise the same as a normal TEI (excluding LEM jettison, obviously). Nixon’s backup speech illustrates this, as it eulogizes those two alone; Collins would have most likely returned on his own in that horrible circumstance barring a further failure of some kind.