First of all, we must say that abominableness (karaha) is something which is not desirable to God, the Almighty but it is also not forbidden. Therefore, one who commits an abominable action will not be punished or reprehended.
As for the narrations which are about anal intercourse, they can be divided into sets:
First, narrations which imply permissibility of anal intercourse, for example, Abdullah bin Abi Ya’fur says: I asked Imam Sadiq (a.s.) about a man who had sex with his wife from the back passage. The Imam answered, “There is no problem and it has been narrated from the Prophet (pbuh) that he said, ‘There is no problem’.[1]
Second, narrations which forbid anal intercourse and which curse the doer of the action[2]as you have mentioned in your message. Therefore, we must endeavor to, somehow, reconcile between these two sets of narrations. The best and most correct way is to accept that it is allowable under certain circumstances and forbidden under others.
a) If wife is consenting to it, it is permissible.
b) It is forbidden, if she is not consenting to it or when it takes place under coercion.
If we are to reconcile between these two sets of narrations, we would say that anal intercourse is abominable in the first instance and it is forbidden in the second. The narrations which forbid anal intercourse are applicable to the second instance.[3] For this reason, we see that some jurisprudents have said: “Anal intercourse is not permissible, as an obligatory precaution, without wife’s consent. If she is consenting, it would be strongly makrooh (abominable).”[4]
 
 

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