I've once heard a story about a pianist of the past who wrote a music piece that critics told him was impossible to play - the length of any person's fingers wouldn't be sufficient. But he used some tool to combat that and make his fingers longer and played that piece successfully. What was his name?
Maybe you are thinking about Robert Schumann who alledgedly used such a device, but damaged his hands beyond repair.
However wikipedia has this to say:
During his studies with Wieck, it has been claimed that Schumann permanently injured a finger on his right hand. Wieck claimed that Schumann damaged his finger by the use of a mechanical device designed to strengthen the weakest fingers, a device which held back one finger while he exercised the others. This claim has been discredited by Clara Schumann, who said that the disability was not due to a mechanical device, and Robert Schumann himself refers to it as "an affliction of the whole hand". Some have argued that, as the disability appeared to have been chronic and have affected the hand, and not just a finger, it was unlikely to have been caused by a finger strengthening device.
The only reference I found was in a discussion of techniques for pianists with small hands, and they only mention medieval_torture -style spacers which forced finger separations (not physical finger extensions) . They also point out that all such gadgets do no good and risk significant injury.
There is a wonderful book called FAMOUS PIANISTS AND THEIR TECHNIQUE which should be read as a history book, not a lesson book. In it the author refers to devices and gimmicks teachers used to stretch, enlarge, calm or strengthen the fingers. Most all with crippling results. Sadly, some of these tricks are still taught today. Just because a teacher says something does not mean it is true, only that that is what they were taught and they are passing it on. A lot of what is taught in lessons is the fake news of pedagogy.
This is a great question and a greater lesson that pianists do not play principally from the fingers but, from the arm. The four and five fingers, for instance, are just as strong as all the other fingers WHEN we align the forearm properly. The fingers do not need strength and endurance, they only need to be used ergonomically, together and moving in the same direction at the same time. Belie the laws of physics and anarchy of strain ensues.