One thing remains here, and that is the basis for the transgression – is it because the nature of it is enjoyment of one's member, like the hadith conveys, restraint from doing it with one's hand but following through with it, for example, if he puts his penis between his thighs until he ejaculates? Or is it the spilling of semen and arousing one's passion in somewhere other than the appointed place, without an excuse, as is conveyed by what he [Al-Haskafi] says here, this being if one does it to stir up desire, etc. ? I am not aware of anyone stating anything about this, although the latter is clearer, since in doing it with the hand of one's wife or someone like her, there is spilling of semen, although it is by enjoyment in a permissible fashion, such as if he ejaculates by thighing or belly rubbing, in contrast to with his own hand or something like that, including if he puts his penis into a wall or something similar until he ejaculates, or if he masturbates with his hand through a barrier that prevents erotic sensation; he transgresses nonetheless. This also attests to what we have said regarding Al-Zayla'i when he concluded that it is not lawful to do it with one's hand, according to the word of the Most High : { And those who guard their crotches } [Al-mu'minun 5] to the end of the verse; he said: Enjoyment has not been made permissible except with these two, that is, with a wife or a slave girl.