I heard Safwan ibn Yahya who has said the following: “I once said to al-Rida’ (a.s.), that one of his followers has asked me to ask you a question in which he feels shy and intimidated. He (the Imam) asked, ‘What is the question?’ I asked, ‘Can a man come to his wife in her anus?’ He (the Imam) said, ‘It is up to him.’ I then asked, ‘Do you do so?’ He (the Imam) said, ‘No, we do not do so.’”