I guess the 3000ft comes from the flight instructors handbook.
“is important that sufficient height is gained to ensure recovery by 3,000 feet above ground level and that
the aeroplane is in the appropriate training area. The pre-stalling check will of course vary from aeroplane to aeroplane, but will normally cover such items as harness, hatches, loose articles, trims, brakes, mixture, carburettor heat, fuel, etc. The student should be provided with and expected to learn such a check list. A turn through 360 degrees to ensure that all is clear around and below
should be carried out immediately prior to commencing the first stall and a 90 degree turn should be carried out before subsequent stalls.”