Ibn Ezra on Leviticus 15:23

ופירוש ואם על המשכב הוא שב אל הכלי אשר תשב עליו והנה הכלי על המשכב או כלי על כלי על כן הטומאה קלה ולא הזכיר לאשה מרכב כי (בהמ׳‎) (ס״א בהווה) דבר הכתוב והמשפט אחד: The meaning of And if he be on the bed (v. 23) refers back to the object⁴⁰I.E. renders And if he (hu) be on the bed as, And if it be on the bed, for the word hu may mean he or it. that she sits upon (v. 22). Now the object⁴¹The object which a person touches. is on the bed or the object⁴²The object which a person touches. is on another object.⁴³Upon which the women sits. The uncleanliness is therefore light.⁴⁴The one who touches it does not have to immerse his garments. Scripture does not mention a saddle with regards to a women for Scripture speaks of what is prevalent.⁴⁵Most of riding was done by men. Some editions read behamah (cattle). According to this version our text reads, for Scripture speaks of [an] animal. The latter is probably to be interpreted, Scripture speaks of one who usually rides on an animal, that is, males, and not females. The law is the same.⁴⁶This law applies to both men and women.