In The Name of Allaah, The Most Merciful, The Bestower of Mercy

Indeed, Allaah is not shy of [stating] the truth, do not approach your women [i.e. sexual intercourse with your wives] in their rectums.”  [Saheeh Al-Jaami Number 933, 934]

Shaikhul Islaam Ibn Taymiyyah [rahimahullaah] said: The rectum is a place of filth [i.e. the exit place of excrement]. Allaah [Glorified be He and free is He from all imperfections] forbids [a husband] from having sexual intercourse with a menstruating woman [i.e. his wife] due to the impurity in her vulva, then how about having sexual intercourse in the place [i.e. rectum] from which [exits] heavy impurity.[Majmoo Al-Fataawaa 32/267]