Our Master al-Sadiq (peace be upon us from him) pointed to the intended meaning of Night and Day in the interpretation of the saying of the Exalted: {By the night when it covers, and the day when it shines} (Al-Layl 1-2) in the chapter of Manifestation from the book Al-Sirat. He said:

"What is meant by that is: if He appears through the Essence, that is through Manifestation (Tajalli). {And the night when it covers} is the Occultation and concealment due to the occurrence of the Trial (Mihna). So He made the Day a proof of the manifestation through the present Person, and the Night a proof of the Occultation..."

Until his saying:

"O Mufaddal, indeed the Night and the Day, which are Manifestation and Occultation, Allah made them eternal so that through them epochs, times, years, months, and days are counted. They are permanent by the permanence of the Pre-eternal (Azal). This is a proof present with the people of expertise, certainty, and realization: that the year, months, weeks, and days are counted within the Day. It is said: 'Such-and-such a day,' because one says 'Friday,' 'the first day of the month,' and 'the first day of the year.' Thus, the Days have names, but the Night has no name. If the night is named, it is only said 'the night of such-and-such,' so it is attributed to the Day.