Tafsir of Qaf 50:18

ما يلفظ

whatever he utters, (in reference to the human),

من قول

of a word, means any word that he or she speaks,

إﻻ لديه رقيب عتيد

but there is a watcher by him ready. means, but there is a scribe whose job is to record it, leaving no word or movement unrecorded. Allah the Exalted said,

وإن عليكم لحفظين

كراما كتبين

يعلمون ما تفعلون

But verily, over you (are appointed angels) to watch you, Kiraman (honorable) Katibin writing down (your deeds), they know all that you do. (82:10-12) Therefore, the scribe records every word that is spoken, according to the explanation of Al-Hasan and Qatadah. This is also the apparent meaning of this Ayah. Imam Ahmad recorded that Bilal bin Al-Harith Al-Muzani said, "The Messenger of Allah said,

إن الرجل ليتكلم بالكلمة من رضوان الله تعالى ما يظن أن تبلغ ما بلغت يكتب الله عز وجل له بها رضوانه إلى يوم يلقاه

وإن الرجل ليتكلم بالكلمة من سخط الله تعالى ما يظن أن تبلغ ما بلغت يكتب الله تعالى عليه بها سخطه إلى يوم يلقاه

Verily, a man might utter a word that pleases Allah the Exalted, unaware of how highly it will be regarded, and on its account Allah the Exalted and Most Honored decrees His pleasure of him until the Day he meets Him. A man might indeed utter a word that angers Allah the Exalted, unaware of how dreadful it will be and on its account Allah the Exalted decrees for him His anger until the Day he meets Him.'' Alqamah used to say, "How many words did I not utter because of the Hadith that Bilal bin Al-Harith narrated.'' At-Tirmidhi, An-Nasa'i and Ibn Majah collected this Hadith. At-Tirmidhi said, "Hasan Sahih.'' There is a Hadith similar to this in the Sahih. Reminding Mankind of the Stupor of Death, the Blast of the Trumpet and the Day of Gathering Allah the Exalted and Most High said,

وجاءت سكرة الموت بالحق ذلك ما كنت منه تحيد