The Prophet ﷺ said: Do not cover the walls. He who sees the letter of his brother without his permission, sees Hell-fire. Supplicate Allah with the palms of your hands; do not supplicate Him with their backs upwards. When you finish supplication, wipe your faces with them. Abu Dawud said: This tradition has been transmitted through a different chains by Muhammad b. Ka'b; all of them are weak. The chain I have narrated is best of them; but it is also weak.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ تَسْتُرُوا الْجُدُرَ مَنْ نَظَرَ فِي كِتَابِ أَخِيهِ بِغَيْرِ إِذْنِهِ فَإِنَّمَا يَنْظُرُ فِي النَّارِ سَلُوا اللَّهَ بِبُطُونِ أَكُفِّكُمْ وَلاَ تَسْأَلُوهُ بِظُهُورِهَا فَإِذَا فَرَغْتُمْ فَامْسَحُوا بِهَا وُجُوهَكُمْ