It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Everything has a place of honour, and the honour of gatherings is that they face the qiblah. And whoever looks into his brother's letter without his permission, it is as if he is looking into the Fire."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10735