The Surah takes its title from the sentence, Wa anzalna' l-hadida, of verse 25.
This is unanimously a Madani Surah, and a study of its subject matter shows that it was probably sent down some time during the interval between the Battle of Uhud and the Truce of Hudaibiyah. This was the time when the tiny Islamic State of Madinah ...
an takhsha'a qulubu- hum li-dhikrillah-i, he says that 17 years after the commencement of the revelation of the Qur'an this verse was sent down to arouse the believers to action. Reckoned thus the period of the revelation of this Surah falls between the 4th and the 5th year after the hijrah....