Ibn Umar misunderstood (the Qur'anic verse, "So come to your tilth however you will")--may Allah forgive him. The fact is that this clan of the Ansar, who were idolaters, lived in the company of the Jews who were the people of the Book. They (the Ansar) accepted their superiority over themselves in respect of knowledge, and they followed most of their actions. The people of the Book (i.e. the Jews) used to have intercourse with their women on one side alone (i.e. lying on their backs). This was the most concealing position for (the vagina of) the women. This clan of the Ansar adopted this practice from them. But this tribe of the Quraysh used to uncover their women completely, and seek pleasure with them from in front and behind and laying them on their backs. When the muhajirun (the immigrants) came to Medina, a man married a woman of the Ansar. He began to do the same kind of action with her, but she disliked it, and said to him: We were approached on one side (i.e. lying on the back); do it so, otherwise keep away from me. This matter of theirs spread widely, and it reached the Messenger of Allah ﷺ. So Allah, the Exalted, sent down the Qur'anic verse: "Your wives are a tilth to you, so come to your tilth however you will," i.e. from in front, from behind or lying on the back. But this verse meant the place of the delivery of the child, i.e. the vagina.  

إِنَّ ابْنَ عُمَرَ وَاللَّهُ يَغْفِرُ لَهُ أَوْهَمَ إِنَّمَا كَانَ هَذَا الْحَىُّ مِنَ الأَنْصَارِ وَهُمْ أَهْلُ وَثَنٍ مَعَ هَذَا الْحَىِّ مِنْ يَهُودَ وَهُمْ أَهْلُ كِتَابٍ وَكَانُوا يَرَوْنَ لَهُمْ فَضْلاً عَلَيْهِمْ فِي الْعِلْمِ فَكَانُوا يَقْتَدُونَ بِكَثِيرٍ مِنْ فِعْلِهِمْ وَكَانَ مِنْ أَمْرِ أَهْلِ الْكِتَابِ أَنْ لاَ يَأْتُوا النِّسَاءَ إِلاَّ عَلَى حَرْفٍ وَذَلِكَ أَسْتَرُ مَا تَكُونُ الْمَرْأَةُ فَكَانَ هَذَا الْحَىُّ مِنَ الأَنْصَارِ قَدْ أَخَذُوا بِذَلِكَ مِنْ فِعْلِهِمْ وَكَانَ هَذَا الْحَىُّ مِنْ قُرَيْشٍ يَشْرَحُونَ النِّسَاءَ شَرْحًا مُنْكَرًا وَيَتَلَذَّذُونَ مِنْهُنَّ مُقْبِلاَتٍ وَمُدْبِرَاتٍ وَمُسْتَلْقِيَاتٍ فَلَمَّا قَدِمَ الْمُهَاجِرُونَ الْمَدِينَةَ تَزَوَّجَ رَجُلٌ مِنْهُمُ امْرَأَةً مِنَ الأَنْصَارِ فَذَهَبَ يَصْنَعُ بِهَا ذَلِكَ فَأَنْكَرَتْهُ عَلَيْهِ وَقَالَتْ إِنَّمَا كُنَّا نُؤْتَى عَلَى حَرْفٍ فَاصْنَعْ ذَلِكَ وَإِلاَّ فَاجْتَنِبْنِي حَتَّى شَرِيَ أَمْرُهُمَا فَبَلَغَ ذَلِكَ رَسُولَ اللَّهِ ﷺ فَأَنْزَلَ اللَّهُ ﷻ { نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ } أَىْ مُقْبِلاَتٍ وَمُدْبِرَاتٍ وَمُسْتَلْقِيَاتٍ يَعْنِي بِذَلِكَ مَوْضِعَ الْوَلَدِ  

[Machine] "Verily, Ibn Umar by Allah's will and intention indeed received forgiveness. Indeed, this neighborhood belonged to the Ansar, who were polytheists, and they were the people of polytheism, whereas this neighborhood belonged to the Jews, who were the people of the Book. They used to witness favors upon themselves and as a result, many people used to follow their actions. It was a custom of the people of the Book not to approach women except on a specific condition. This was to conceal the woman's status. Thus, this Ansari neighborhood adopted this practice from them. This neighborhood, however, belonged to the Quraish who used to unlawfully unveil women and take pleasure in them, whether they were facing them or their backs. When the migrants arrived in Medina, a man among them married a woman from the Ansar neighborhood and indulged in this practice with her. She refused it and said, 'We were accustomed to a specific condition, so follow it or keep away from me until their matter is settled.' The Messenger of Allah ﷺ was informed about this. So, Allah the Exalted revealed the following verse: "Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish" [Quran 2:223]. It means that whether they face you or turn their back to you, that is the site for procreation."  

إِنَّ ابْنَ عُمَرَ وَاللَّهُ يَغْفِرُ لَهُ وَهَمَ إِنَّمَا كَانَ هَذَا الْحَيَّ مِنَ الْأَنْصَارِ وَهُمْ أَهْلُ وَثَنٍ مَعَ هَذَا الْحَيِّ مِنَ الْيَهُودِ وَهُمْ أَهْلُ كِتَابٍ كَانُوا يَرَوْنَ لَهُمْ فَضْلًا عَلَيْهِمْ فَكَانُوا يَقْتَدُونَ بِكَثِيرٍ مِنْ فِعْلِهِمْ وَكَانَ مِنْ أَمْرِ أَهْلِ الْكِتَابِ أَنْ لَا يَأْتُوا النِّسَاءَ إِلَّا عَلَى حَرْفٍ وَاحِدٍ وَذَلِكَ أَسْتَرُ مَا تَكُونُ الْمَرْأَةُ فَكَانَ هَذَا الْحَيُّ مِنَ الْأَنْصَارِ قَدْ أَخَذُوا بِذَلِكَ مِنْ فِعْلِهِمْ وَكَانَ هَذَا الْحَيُّ مِنْ قُرَيْشٍ يَشْرَحُونَ النِّسَاءَ شَرْحًا مُنْكَرًا وَيَتَلَذَّذُونَ مِنْهُنَّ مُقْبِلَاتٍ وَمُدْبِرَاتٍ وَمُسْتَلْقِيَاتٍ فَلَمَّا قَدِمَ الْمُهَاجِرُونَ الْمَدِينَةَ تَزَوَّجَ رَجُلٌ مِنْهُمُ امْرَأَةً مِنَ الْأَنْصَارِ فَذَهَبَ يَصْنَعُ بِهَا ذَلِكَ فَأَنْكَرَتْهُ عَلَيْهِ وَقَالَتْ إِنَّمَا كُنَّا نُؤْتَى عَلَى حَرْفٍ وَاحِدٍ فَاصْنَعْ ذَلِكَ وَإِلَّا فَاجْتَنِبْنِي حَتَّى سَرَى أَمْرُهُمَا فَبَلَغَ ذَلِكَ رَسُولَ اللَّهِ ﷺ فَأَنْزَلَ اللَّهُ تَبَارَكَ وَتَعَالَى {نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ} [البقرة 223] «أَيْ مُقْبِلَاتٍ وَمُدْبِرَاتٍ وَمُسْتَلْقِيَاتٍ يَعْنِي ذَلِكَ مَوْضِعَ الْوَلَدِ»