Tafsir of Al-Qalam 68:18

It is said: meaning they do not say, "If Allah the Exalted wills." Calling this an exception is valid, even though it is a condition, in that its implication is the same as that of an exception. For your saying, "I will surely go out, if Allah the Exalted wills," and "I will not go out unless Allah wills," have the same meaning. The Imam said: The root of istithna (exception) is thani, which means to turn back or avert. Thus, restricting [a statement] with a condition is a turning back of the binding nature of that oath; therefore, applying the term "exception" to it is literal.

It is also said: meaning they do not turn back from what they intended regarding withholding [the harvest] from the poor. According to both interpretations, the apparent meaning is that it is a conjunction connected to "they swore." The requirement of the apparent construction would have been "and they did not make an exception" (wa ma istathnaw). It is as if the shift [to the present tense] was employed to bring the scene to mind, due to the strangeness it contains, for the appropriate action when swearing upon something that necessitates the abandonment of an act of obedience is to make an exception.

In al-Kashf, it is stated that it is a circumstantial qualifier (hal), meaning "without making an exception." The shift to the present tense serves as a form of expression and an alert to the magnitude of their error, and it contains an allusion to what we have mentioned.

It is also said: the meaning is that they do not set aside the share of the poor, just as their father used to set it aside. According to this, it is linked to His saying, "so that he might harvest it," and it is something sworn upon, or it is linked to His saying, "in the early morning," as a circumstantial qualifier. This is a meaning against which there is no objection.