حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ عُثْمَانَ بْنِ الْأَسْوَدِ، عَنْ مُجَاهِدٍ، قَالَ: "مَنْ أَتَى امْرَأَتَهُ فِي دُبُرِهَا فَهُوَ مِنْ الْمَرْأَةِ مِثْلُهُ مِنْ الرَّجُلِ، ثُمَّ تَلَا: وَيَسْأَلُونَكَ عَنِ الْمَحِيضِ قُلْ هُوَ أَذًى فَاعْتَزِلُوا النِّسَاءَ فِي الْمَحِيضِ وَلا تَقْرَبُوهُنَّ حَتَّى يَطْهُرْنَ فَإِذَا تَطَهَّرْنَ فَأْتُوهُنَّ مِنْ حَيْثُ أَمَرَكُمُ اللَّهُ سورة البقرة آية 222، أَنْ تَعْتَزِلُوهُنَّ فِي الْمَحِيضِ: الْفَرْجَ، ثُمَّ تَلَا: نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ سورة البقرة آية 223 قَائِمَةً، وَقَاعِدَةً، وَمُقْبِلَةً، وَمُدْبِرَةً فِي الْفَرْجِ".
Mujahid (may Allah have mercy on him) said: Whoever has intercourse with his wife in her anus, it is equivalent to intercourse with a man (i.e., sodomy). As evidence, he recited the verse: "And they ask you about menstruation. Say: It is harm, so keep away from women during menstruation and do not approach them until they are pure. But when they have purified themselves, then go to them from where Allah has ordained for you." [البقره 222/2] In this, it is clarified that during menstruation, keep away from women, that is, from the vagina. Then he recited this verse from Surah Al-Baqarah: "Your wives are your fields, so come to your fields as you wish." He explained that whether standing, sitting, lying on the back, or lying face down (on the stomach), in whatever way you wish, only have intercourse in the vagina (the private part from where menstruation comes, only there).