What is the ruling on dedicating a thin, soft prayer mat for the forehead to prevent the appearance of a callus, while still enabling the forehead to touch the ground?

We have previously clarified the permissibility of prostrating on a mat, on the turban's folds, on the edge of a garment or cloth, on the ground, and on a rug.

As for specifically dedicating the forehead to what one prostrates on, some scholars have explicitly stated its detestability, and that it is a mark of the people of innovation (Ahl al-Bid'ah), as mentioned by Ibn Muflih and Al-Buhuti.