Translation of the verse 18 from Surah At-Takwir : Number of verses 29 - - page 586 - Part 30.
And by the dawn as it brightens;
And by the dawn when it breathes
(81:18) and the morn as it breathes. *13
*13) That for which the oath has been sworn, has been stated in the following verses. The oath means: "Muhammad (upon whom be Allah's peace and blessings) has not seen a vision in darkness, but when the stars had disappeared, the night had departed and the bright morning had appeared, he had seen the Angel of God in the open sky. Therefore, what he tells you is based on his own personal observation and on the experience that he had in full senses in the full light of day."
Source : At-Takwir Verse 18: And by the dawn when it breathes