Ok I spent the last hour looking for this interview and I honestly can't find it - the closest I can get to the source is this article saying that Russia is building a strategic reserve of tanks:
But it's not the one I read which was literally a general saying "they are building tanks and not sending them to the front - why if not to fight with NATO eventually".
> Russian factories are working at full speed, producing new tanks and repairing those that have been dusty for years," writes "Le Figaro". The French daily refers to its sources and data from independent study groups. On the other hand, experts also point to the fact that this year the losses of the Russians have decreased - this year it was only 200 tanks. According to the newspaper, this may be due to the fact that the participation of these vehicles in the fighting at the front has been reduced. This, in turn, is the result of greater use of drones.
This actually strikes me as fairly plausible: it suggests that Russia has decided that tanks are not ideally suited for the current drone war in Ukraine. So they're continuing to ramp up production, but aren't (at this point) sending them to the front.
This doesn't necessarily mean that they have a long-term plan to invade NATO, however. I can think of many other scenarios where it would be in Russia's strategic interest to have a large modernized tank force in reserve.
https://wiadomosci.gazeta.pl/wiadomosci/7%2C114881%2C3206584...
But it's not the one I read which was literally a general saying "they are building tanks and not sending them to the front - why if not to fight with NATO eventually".