Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Cursed is the one who has anal intercourse with his wife."
شرح الحديث :
This Hadīth contains a severe warning for whoever resorts to anal intercourse with his wife. This results in a person’s expulsion from the mercy of Allah, the Exalted. This shows that anal intercourse is a major sin, and it is therefore impermissible for a Muslim to do it.