What is Eavesdropping?
Eavesdropping/spying is the act of secretly listening to the private conversation of others without their knowledge and permission. Eavesdropping is wrong and no one likes for others to listen in one their private conversations. It can cause friendships to break and hurt feelings. In fact, it is strictly forbidden in Islam.
It is narrated in al-Saheehayn from Abu Hurayrah that the Prophet (peace and blessings of Allaah be upon him) said: ‘Beware of suspicion, for suspicion is the falsest of speech. Do not eavesdrop; do not spy on one another; do not envy one another; do not forsake one another; do not hate one another. Be, O slaves of Allaah, brothers.”
Al-Bukhaari, 5144; Muslim, 2563.
"O you who believe! avoid most of suspicion, for surely suspicion in some cases is a sin, and do not spy nor let some of you backbite others. Does one of you like to eat the flesh of his dead brother? But you abhor it; and be careful of (your duty to) Allah, surely Allah is Oft-returning (to mercy), Merciful."