In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
The Prophet [sallal-laahu-alayhi-wasallam] said, “Whoever listens to the talk of some people who do not like him [to listen] or they run away from him, then molten lead will be poured into his ears on the Day of Resurrection. [Sahih Al-Bukhaari Number 7042].
Shaikh Zaid Bin Haadi [rahimahullaah] said:
It may be that two or more people gather to speak about a particular affair that concerns them, and they do not want anyone else to know about it; but then a person or more than one person becomes an obstacle by listening to their speech and [wants] to know what they are talking about, whilst they are not pleased with that. This is an act of transgression and foolishness – that a person involves himself into something that does not concern him. And from the perfection of a person’s Islaam is to leave that which does not concern him. However, there is an exception to this prohibition such as when a person listens into the speech of those who are focused or [involved] in seeking to breach the state of safety and security of the Muslims.
[An Excerpt from ‘Awnul Ahadis Samad Sharh Al-Adabil Mufrad’ Vol 3 page 281]