Tafsir of Al-Muzzammil 73:7

"Indeed, you have in the day a prolonged sabhan," meaning: movement, engagement in your tasks, and preoccupation with your concerns, such that you are unable to devote yourself to worship; therefore, occupy yourself with it during the night. The root of al-sabh is swift movement in water, then it was metaphorically applied to movement in a general sense, as stated by al-Raghib, who cited the poet’s verse:

They have permitted for you the east of the land and its west, So for you therein, O companion, is a place to roam (sabh) from the places to roam (al-subuh).

This is an explanation of the external motivation for rising at night, following the explanation of the internal motivation previously mentioned.

It is also said: It means you have during the day leisure and capacity for your sleep and your dealings with your needs. Others said: If you miss any part of the night, you have leisure during the day in which you can make up for it; thus, al-sabh refers to leisure, a usage supported linguistically, though the first interpretation is more consistent with the meaning of "swimming in water" and more appropriate to the context.

Furthermore, this statement is either a completion of the rationale, making it easier for him by suggesting the day is suitable for rest, so he should seize the night for worship and be grateful that he was not tasked with both for worship; or it is an emphasis on safeguarding the night vigil, implying that if it is missed, it must be made up during the day, for there is capacity in it for that. In this, there is an allusion to the meaning of making the night and day follow one another.

Ibn Ya‘mur, ‘Ikrimah, and Ibn Abi ‘Ablah read it as sabkhan (with a dotted kha), meaning: dispersion of the heart with preoccupations, a metaphor derived from sabkh al-suf (teasing wool), which is pulling it apart and spreading its fibers. Many others said it refers to a lightening of burdens. Al-Asma‘i stated: It is said, "May Allah sabakha your fever," meaning: lighten it. In the Hadith, it is said: "Do not tusbakhi (lighten) your supplication," meaning do not make it light. From this is the saying: "So lighten (fasbikh) your grief, and know that if the Most Merciful decrees something, it will come to pass."

It is also said that al-sabkh is stretching; it is said, "Stretch (sabkhi) your cotton," meaning extend it. The pieces of cotton are called saba'ikh, the singular being sabkhah. From this is the saying of al-Akhtal, describing a hunter and dogs: "They released them, scattering the dust just as one scatters the fibers (saba'ikh) of cotton teased by bowstrings."

The author of al-Lawamih stated that Ibn Ya‘mur and ‘Ikrimah interpreted sabkhan (with a dotted kha)—after having read it as such—by saying it means sleep; that is, he sleeps during the day to aid himself in the night vigil. This reading may permit meanings other than this, but since they interpreted it as such, we shall not deviate from it. Perhaps this is an interpretation based on the necessary consequence.