The rule is “Keep your finger off the trigger until your sights are on the target.” During the act of placing a handgun in a holster the muzzle is, by definition, off of the target. It’s essential to keep the trigger guard clear as the pistol is placed into the holster.

The picture depicts a polymer holster into which a gunshot was fired. The expended round shown in the picture is nicely expanded. It was found on the ground near the shooter who holstered the autopistol with finger on the trigger. It clearly passed through the shooter’s leg before coming to rest on the ground.

Keep your finger off the trigger until your sights are on the target.