There should be limits in the sexual life of spouses. It is expressed in Qur’an that the main purpose of sexual intercourse is to procreate and that the position of intercourse is let free as long as it is through the woman’s reproductive organ. The Glorified Allah commands:
“They ask you about menstruation. Say: It is a discomfort. Therefore keep aloof from the women during menstruation and do not approach them until they are clean. When they have thoroughly cleansed themselves, then come to them from where Allah has ordained for you. Indeed, Allah loves those who are constantly repentant and loves those who purify themselves. Your wives are (like) a cropland for you. So go to your croplands as you please and make yourselves ready for it. Fear Allah! Know that you are to meet Him and give good tidings to the believers.” (Al-Baqarah/ The Cow 2:222-223)
Cropland is a place to harvest. Since reproduction is not possible through anal sex, the verse forbids it. According to these verses, Allah commands regular way of intercourse.
Narrations related to this topic also express that anal sex is forbidden:
“Cursed is the one who approaches his wife in her rectum.” (Abu Dawood, Nikah, 45, Ahmed b. Hanbal, 2/444)
“… Do not approach your women in their rectums. Allah does not refrain from telling the righteousness.” (Tirmidhi, Rada’, 12)
“The Glorified Allah will not look at a man with an eye of mercy who has intercourse with a man or a woman through the anus” (Tirmidhi, Rada’, 12; Ibn Majah, Nikah, 29)
It is not for a Muslim to have intercourse in the forbidden way instead of the commanded one while knowing it is forbidden. Although anal sex is forbidden, nobody would stay impure (junub) forever due to this action. One should repent and never perform the same action again.