Allah سبحانه وتعالى says in the Holy Qu’ran:
مَا يَلْفِظُ مِن قَوْلٍ إِلَّا لَدَيْهِ رَقِيبٌ عَتِيدٌ
For every word that we utter, an angel is ever-eager to record it. We should act on everything that we learn, especially with regard to remaining silent.
The less a person exposes his eyes and ears to the dunya, the more that his heart will eventually follow suit. Similarly, the impact of the tongue upon the heart is such that when the tongue speaks the heart has no choice but to listen, but if the tongue remains silent, the heart will then “speak” , i.e. when the activities of the outer organs like the tongue are curbed and stopped the heart will remain free for its activities such as remembrance of Allah سبحانه وتعالى and contemplation.
[This short excerpt is based on a brothers' majlis (gathering for spiritual training) held by Shaykh Abu Yusuf Riyadh ul Haq on 22nd March 2000 and 25th March 2000].