Surah Yunus, Ayat 16-17

Ayat 16. Say (O Muhammad  [SAWW](PBUH) : "If Allah had so willed, I should not have recited it to you nor would He have made it known to you. Verily, I have stayed amongst you a life time before this. Have you then no sense?"

Ayat 17. So who does more wrong than he who forges a lie against Allah or denies His Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.)? Surely, the Mujrimun (criminals, sinners, disbelievers and polytheists) will never be successful! 

Hazrat Wabisah bin Mabad (May Allah be pleased with him) reported: I went to Messenger of Allah [SAWW](PBUH) and he asked me, "Have you come to inquire about piety?'' I replied in the affirmative. Then he said, "Ask your heart regarding it. Piety is that which contents the soul and comforts the heart, and sin is that which causes doubts and perturbs the heart, even if people pronounce it lawful and give you verdicts on such matters again and again.'' [Masnad Ahmad, Imam Ahmad Hadith # 228/4].  

Lesson : as mentioned above in Surah Yunus Ayat 17. "So who does more wrong than he who forges a lie against Allah or denies His Ayat". There are two points about this Hadith. First, it is one of the miracles of Messenger of Allah [SAWW](PBUH) who discovered the nature of the question before it was put to him. Second, man's heart is the biggest guide to him and he, therefore, should keep his heart illuminated with the light of Faith so as to continue receiving guidance from it.