Cursed is the one who approaches his wife in her…..
The Messenger of Allaah (sallal-laahu alayhi wasallam) said:
”Cursed is he who approaches a woman (i.e. his wife) in the anus.” 
The messenger (sallal-laahu- alayhi wasallam) said:
”Indeed Allah is not shy of the truth. Do not have intercourse with women (i.e. your wives) in their anuses.” 
Reported by Imaam Ahmad 2/479.Saheeh al Jaami no: 5865
 Reported by Imam Nasaa-ee, Ibn Maajah and others. Authenticated by Imaam Al Albaanee in Saheeh al Jaami No: 933, 934, 1852, 7711