Surah 50. Qaf, Ayah 18

I.e., his conscience. The "uttering of a word" is conceptually connected with the "whispering" within man's psyche spoken of in the preceding verse.

 The angel to the right records the good deeds of each person, while the one to the left records every evil deed. They always accompany the person at all times, except when one uses the toilet or is intimate with their spouse.

Then each "word" spoken is taken down by a guardian (raqib). This has been construed to mean that the guardian only records words, not thoughts which are not uttered. Thoughts may be forgiven if not uttered, and still more if they do not issue in action. At the stage at which we clothe a thought in words, we have already done an action. The Recorders mentioned in the last verse make a complete Record, in order to supply motives and springs of action, which will affect the degrees or status in the Hereafter. The three together, individuals or kinds, make the honourable Recorders, Kiraman Katibin, (plural, not dual number) mentioned in lxxii. 11.