We created man and We know what his own self whispers to him. We are nearer to him than his jugular vein. (Sura Qaf: 16)
God is so near to man that He hears the prayer of everyone—even if he prays inwardly—and it is He Who answers it:
If My servants ask you about Me, I am near. I answer the call of the caller when he calls on Me. They should therefore respond to Me and believe in Me so that hopefully they will be rightly guided. (Sura alBaqara: 186)
God knows what a person harbours in his heart. He knows whether he engages in a deed to earn His consent, or to satisfy his own lower soul. God reminds us that He knows our inner thoughts:
...Know that God knows what is in your selves, so beware of Him! And know that God is Ever-Forgiving, All-Forbearing. (Sura al-Baqara: 235)
Though you speak out loud, He knows your secrets and what is even more concealed. (Sura Ta Ha: 7)
God's Messenger, the Prophet Muhammad (saas) also reminded Muslims when they prayed that God is very close to them by saying, "You are calling a Hearer, One very close by; The One Who you are calling is closer to each one of you."(Al-Bukhari and Muslim)
As He is with you at every moment, God is with you as you are reading this book; He sees what you are doing and knows what you are thinking. This fact is related in the Qur'an as follows:
Do you not see that God knows what is in the heavens and on the earth? Three men cannot confer together secretly without Him being the fourth of them, or five without Him being the sixth of them, or fewer than that or more without Him being with them wherever they are. Then He will inform them on the Day of Rising of what they did. God has knowledge of all things. (Sura al-Mujadala: 7)