Ibn Mas'ud reported God’s messenger as saying, “God has propounded as a parable a straight path on the sides of which are walls with open doors over which curtains are hanging down. At the top of the path there is one who calls, ‘Go straight on the path and do not follow an irregular course.’ Above that one is another who calls out as often as anyone tries to open any of those doors, ‘Woe to you! do not open it, for if you open it you will go through it.’” He then interpreted it telling that the path is Islam, the open doors are the things God has forbidden, the curtains hanging down are the limits God has set, the crier at the top of the path is the Qur’an, and the one above him is God’s monitor in every believer’s heart. Razin and Ahmad transmitted it. Baihaqi transmitted it in Shu'ab al-iman from an-Nawwas b. Sim'an, as did Tirmidhi in a more concise form.