At idle? No. There is zero load on the engine, so it's the least-stressed time.
Low RPM? Possibly. Cruising along at 70mph in 6th in something with a big V8 will give you an RPM of around 1500rp which most would consider low, but is by design. No issues there at all. However, if you're trying to pull hard from that kind of RPM in a high gear then yes, that's the worst possible thing to do as it'll be severely straining the drivetrain. It also sounds and feel horrible, which is why no-one really does it (think 30mph in 6th in the Zed: Doable, but if you try and accelerate the car hates it!). My 911 will be in 7th by 45mph, but if you try and accelerate to any degree in auto mode it'll drop a couple of gears to assist.