The division of the Qur'an into chapters, like its division into verses, is mentioned in the Qur'an itself. In several places God uses the actual words "surah" and "ayat". In (XXIV:1) He says "(Here is) a surah which we have revealed," in "Repentance", verse 86, "And when a surah is revealed," in "The Cow" verse 23, "Then produce a surah like it... " and other similar verses.
The name of the chapter is sometimes derived from a name or form occurring in the chapter or from a subject treated by the chapter; for example "The Cow", "The Family of 'Imran", "The Night Journey" and "The Unity". We may note here that in the old Qur'ans it is usual to observe the following at the beginning of each chapter: "The surah in which the Cow is mentioned" or "the surah in which the family of Imran is mentioned. " Sometimes the chapter becomes known by its first phrase; take for example, the chapter "Read in the name of your Lord" (or "the Clot") or the chapter, "Truly we revealed it" (The Night of Power) or the chapter "Those who disbelieve" (also called "The Clear Proof").
Sometimes the chapter becomes known by a certain position or quality it possesses; thus the chapter "The Opening of the Book" or "The Mother of the Book" or "The Seven Oft-repeated verses" (all describing the first chapter, or the "al-Fatihah"). The chapter "The Unity" is also called by the name "al-Ikhlas" (meaning that it describes the absolute unity of God) or by the name "Nisbat al-Rabb" (meaning the chapter which describes the divine nature of the Lord in relation to the slave). This method of naming the chapters was also used in the early days of Islam and is attested to by the traditions. There are traditions, whose chains of authority reach back to the Prophet, which assert that the name of such chapters as "The Cow", "The Family of 'Imran", "Hud" and "The Event" were used by the Prophet himself. We may conclude from this that many of these names came into being at the time of Prophet as a result of being in common use