Almighty Allah teaches Prophet Muhammad, Peace Be upon Him, to mention Allah's name and pray a lot if His chest is constrained by the hostility of His enemies and their plotting. There are two verses in the Quran which reveal that meaning.
Allah says: "And We already know that your breast is constrained by what they say. So exalt [Allah] with praise of your Lord and be of those who prostrate [to Him]." (Al-Hijr: 97-98).