Each time we sleep with a Houri we find her virgin. Besides, the penis of the Elected never softens. The erection is eternal; the sensation that you feel each time you make love is utterly delicious and out of this world and were you to experience it in this world you would faint. Each chosen one [i.e. Muslim] will marry seventy [sic] houris, besides the women he married on earth, and all will have appetizing vaginas.
Al-Itqan fi Ulum al-Qur'an, p. 351