In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah [The Most High] said:
وَلَقَدْ خَلَقْنَا الْإِنسَانَ وَنَعْلَمُ مَا تُوَسْوِسُ بِهِ نَفْسُهُ ۖ وَنَحْنُ أَقْرَبُ إِلَيْهِ مِنْ حَبْلِ الْوَرِيدِ
إِذْ يَتَلَقَّى الْمُتَلَقِّيَانِ عَنِ الْيَمِينِ وَعَنِ الشِّمَالِ قَعِيدٌ
مَّا يَلْفِظُ مِن قَوْلٍ إِلَّا لَدَيْهِ رَقِيبٌ عَتِيدٌ
And indeed We have created man, and We know what his ownself whispers to him. And We are nearer to him than his jugular vein [by Our Knowledge]. [Remember!] that the two receivers [recording angels] receive [each human being after he or she has attained the age of puberty], one sitting on the right and one on the left [to note his or her actions]. Not a word does he [or she] utter, but there is a watcher by him ready [to record it]. [Surah Qaaf, Aayaat 16-18]
Allaah [The Most High] informed [us] that He alone created human beings – males and females, and He knows all their state of affairs. He knows everything that is hidden about them and what their own souls whisper to them. He [The Most High] is nearer to them than their jugular veins by His knowledge, even though the jugular vein is the closest thing to the human. Therefore, this should make the human mindful of Allaah, Who knows all the hidden affairs in the soul and heart of the human being in all circumstances. This should also make the human being shy in the presence of Allaah, that he [or she] is not seen committing what Allaah has forbidden or abandoning what Allaah has commanded.
[Source: An Excerpt from ‘Tayseer Al-kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan’. Slightly paraphrased]