The Sun and the Moon [move] by a reckoning.

The prepositional phrase constitutes the predicate, with an implied noun—that is, "The Sun and the Moon" exist or are settled "by a reckoning." Alternatively, the predicate is omitted, and the prepositional phrase is connected to it, meaning: they move by a reckoning.

Husban is a verbal noun, similar to ghufran, meaning calculation, as stated by Qatadah and others. That is, they move by a calculated measure in their zodiacal signs and mansions, such that the affairs of terrestrial beings are organized by it, the seasons and times differ, and years and accounts are known.

Al-Dahhak and Abu Ubaidah said: It is the plural of hisab (calculation), like shuhban [is the plural of] shihab. This means they move according to various calculations in their zodiacal signs and mansions.

Mujahid said: Al-husban is the rotating sphere, derived from the husban of a millstone—which refers to the circular edges surrounding it. On this view, the letter ba indicates container-ship (vessel/location), and the prepositional phrase occupies the position of the predicate without needing the aforementioned assumption. The intended meaning is that both the Sun and the Moon are in a sphere.

The majority hold the first view, and the movement of the Sun and the Moon is something that should not be doubted. The philosophers of the age used to claim that the Sun does not move at all, that the Moon moves around the Earth, and that the Earth moves around the Sun. We have heard that for several years they have retracted from that, claiming now that the Sun has a motion [relative] to another star. This indicates that they possessed no proof for their initial claim, contrary to what those who championed them used to say. It is apparent that their state today—and indeed, tomorrow—is like their state of yesterday. We remain with the literal appearances until definitive proof of their contradiction is established; only then shall we incline toward interpretation, for its door is wide. A statement similar to this is His saying: [...]