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  

"سَلُوا اللهَ بِبُطُونِ أَكُفَّكُمْ، وَلَا تَسْأَلُوه بِظُهُورِهَا، فَإِذَا فَرغْتُم فَامْسَحُوا بِهَا وُجُوهَكُمْ".