Musnad Ahmad 655
It was narrated that `Ali (رضي الله عنه) said:
A Bedouin came to the Prophet (ﷺ) and said: O Messenger of Allah, what if we are in the desert and a little wind comes out of one of us? The Messenger of Allah (ﷺ) said: “Allah, may He be glorified and exalted, not too shy to tell the truth. If one of you does that, let him do wudoo`. And do not approach women in their back passage [and once he said: in their anuses].`
حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ مُسْلِمٍ الْحَنَفِيُّ، عَنْ أَبِيهِ، عَنْ عَلِيٍّ، رَضِيَ اللَّهُ عَنْهُ قَالَ جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ يَا رَسُولَ اللَّهِ إِنَّا نَكُونُ بِالْبَادِيَةِ فَتَخْرُجُ مِنْ أَحَدِنَا الرُّوَيْحَةُ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّ اللَّهَ عَزَّ وَجَلَّ لَا يَسْتَحْيِي مِنْ الْحَقِّ إِذَا فَعَلَ أَحَدُكُمْ فَلْيَتَوَضَّأْ وَلَا تَأْتُوا النِّسَاءَ فِي أَعْجَازِهِنَّ وَقَالَ مَرَّةً فِي أَدْبَارِهِنَّ‏.‏