Surah ad-Duha (The Morning Brightness) 93 : 2

Its subject matter clearly indicates that it belongs to the earliest period at Makkah. Hadith also show that the revelations were suspended for a time, which caused the Prophet to be deeply distressed and grieved. On this account he felt very anxious that perhaps he had committed some error because of which his Lord had become angry with him and had forsaken him. Thereupon he was given the consolation that revelation had not been stopped because of some displeasure but this was necessitated by the same expediency as underlies the peace and stillness of the night after the bright day, as if to say: “If you had continuously been exposed to the intensely bright light of Revelation (Wahi) your nerves could not have endured it. Therefore, an interval was given in order to afford you peace and tranquillity.” This state was experienced by the Prophet in the initial stage of the Prophethood when he was not yet accustomed to hear the intensity of Revelation. On this basis, observance of a pause in between was necessary. This we have already explained in the introduction to Surah 74: al-Muddathir (The Cloaked One).