Hardening of the Heart

The Prophet (sal Allahu alaihi wa sallam) said: "Do not speak much without mentioning Allah, for too much speech without mentioning Allah hardens the heart, and the hard hearted are the furthest of all people from Allah Most High." [Tirmidhi]

Imam Nawawi explains: "Every legally responsible person should refrain from saying anything except when there is a clear advantage to speaking. Whenever speaking and not speaking are of equal benefit, it is sunnah to remain silent, for permissible speech easily leads to that which is unlawful or offensive, as actually happens much or even most of the time -- and there is no substitute for safety. The Prophet (peace be upon him) said, ‘whoever believes in Allah and the Last Day, let him say what is good or remain silent.’ (Authenticated by Imams Bukhari and Muslim)" [r 1.1: Reliance of the Traveller by Ahmad ibn Naqib al-Misri]