Musnad Ahmad

It is narrated from Hazrat Nawas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: Allah has given an example that there is a straight path, on both sides of which are walls. In these walls are open doors, and curtains are hanging over the doors. At the main gate of the path, a caller is standing and saying: O people! All of you enter into it and do not scatter to the right or left. And a caller is calling in the middle of the path; when anyone wants to open one of these doors, he says to him: Do not open it, for if you open it, you will enter it. The straight path refers to Islam, the walls refer to the limits set by Allah, the open doors are the forbidden things, and the caller at the main gate of the path is the Noble Qur’an, and the caller in the very middle of the path is an admonisher from Allah in the heart of every Muslim (which is called conscience).