Sahih Bukhari Volume 6, Book 60, Hadith Number 341.
Narrated By ‘Abdullah : There gathered near the House (i.e. the Ka’ba) two Quraishi persons and a person from Thaqif (or two persons from Thaqif and one from Quraish), and all of them with very fat bellies but very little intelligence. One of them said, “Do you think that Allah hears what we say?” Another said, “He hears us when we talk in a loud voice, but He doesn’t hear us when we talk in a low tone.” The third said, “If He can hear when we talk in a loud tone, then He can also hear when we speak in a low tone.” Then Allah, the Honorable, the Majestic revealed:
‘And you have not been screening against yourself lest your ears, and eyes and your skins should testify against you…’ (41.22-23)