Allah said:

(...as Allah has ordained for you.) this refers to Al-Farj (the vagina), as Ibn `Abbas, Mujahid and other scholars have stated. Therefore, anal sex is prohibited, as we will further emphasize afterwards, Allah willing. Abu Razin, `Ikrimah and Ad-Dahhak and others said that:

(...then go in unto them as Allah has ordained for you.) means when they are pure, and not during the menses. Allah said afterwards:

(Truly, Allah loves those who turn unto Him in repentance) from the sin even if it was repeated,

(and loves those who purify themselves.) meaning, those who purify themselves from the impurity and the filth that include having sexual intercourse with the wife during the menses and anal sex.