What is the ruling when a husband divorces his menstruating wife by saying, 'You are divorced according to the Sunnah immediately'?

Primary text

If a husband tells his menstruating wife, 'You are divorced according to the Sunnah immediately,' the description (according to the Sunnah) is nullified, and the divorce occurs immediately. This is because he described the divorce pronouncement with a quality (Sunnah) that divorce during menstruation does not possess.