كتاب الطهارة وسننها
Read the English translation first, with the original Arabic directly underneath.
It was narrated from Abu Sa`eed al-Khudri that:
The Messenger of Allah said: "No two people should converse while relieving themselves, each of them looking at the private parts of the other, for Allah, the Mighty and Sublime, hates that." (Da'if) Other chains with similar wording.
لاَ يَتَنَاجَى اثْنَانِ عَلَى غَائِطِهِمَا يَنْظُرُ كُلُّ وَاحِدٍ مِنْهُمَا إِلَى عَوْرَةِ صَاحِبِهِ فَإِنَّ اللَّهَ عَزَّ وَجَلَّ يَمْقُتُ عَلَى ذَلِكَ