“(Narrated) Muhammad bin Yahya , from Ahmad bin Muhammad, from Ali bin al-Hakam said: I heard Safwaan bin Yahya saying: I said to (Imam) al-Rida : a man among your followers requested me to ask you about a matter, which he feared and embarrassed to ask you (directly). He said: What is it? I said: For the man to use the woman’s anus. He said: he may. I said: Do you personally do that? He said: We do not do that.”
[al-Kafi (fil Furoo’): al-Kulainy, Book of Nikaah, Chapter: Women’s anuses, vol.5, p.540, narration 2.]
“(Narrated) al-Hussain bin Ali bin Yaqteen said: I asked Abul-Hassan about the permissibility for the man to have anal sex with women, he said: it was made halal (permissible) in the Book of Allah, when (Prophet) Lot said: 11:78 Here are my daughters, they are purer for you and he knew it was not the vagina they were after.”
[Tafseer al-Ayyashi, vol.1, p.157; Bihaar al-Anwaar vol.21, p.98; Tafseer al-Burhaan vol.2, p.230]
Narrated Abdullah bin Abi Ya’foor: I asked Abu Abdullah about approaching women thru their anus, he said: no Problem. He then recited: 2:223 Your women are as tilth unto you, so approach your tilth when (or how) ye will.”
[Tafseer al-Ayyashi, vol.1, p.110; Bihaar al-Anwaar Baqir al-Majlisi, vol.23, p.98; al-Burhaan fee Tafseer al-Qur’an: Hashim al-Bahraani, vol.1, p.219; Wasaa’il al-Shi’a: al-Hur al-Amily, vol.3, chpater 73: An-Nikaah wa Aadabuh]