Crouch on rightmost pixel of the ledge to the left of the door, jump then move over quickly without spin jumping. The timing for the forward press needs to be between 0 and 5 frames after pressing jump (a 6-frame window). Samus's subpixel position is important: X position needs to be at least $64.4000, this is the rightmost 75% of the rightmost pixel. Morph provides an easier setup. From below the ledge, press left against the wall, jump, mid-air morph, and tap left to move slightly onto the ledge.