Tafsir of Ta-Ha 20:106

The matter of the fa (ف) in His saying, "Then He will leave it" (fayadharuha), is very apparent. The pronoun refers either to the mountains, considering their lower parts that remain after the pulverization, which are their foundations and centers—meaning: He will leave what became leveled of them, its surface becoming equal to the surfaces of the rest of the parts of the earth after pulverizing what rose and jutted out from them. Alternatively, it refers to the earth, indicated by the context of the situation, as it remains after the pulverization of the mountains. Upon both estimations, He—Glorified be He—leaves everything as "a level plain, smooth."

For when the mountains are leveled and their surfaces are made equal to the surfaces of the parts of the earth, the whole is made into a single surface.

"The Qa'" (قاعا): It is said to be the plain. Al-Jawhari said: It is the level part of the earth, and from this is the saying of Dirar ibn al-Khattab: "We shall be at the lowlands, [O] Quraysh, like the plain-dwellers in the palms of slave girls." Ibn al-A'rabi said: It is the smooth land that has no vegetation and no buildings. Makki reported that it is the exposed place. It is also said to be the hard, level part of the earth, and it is said to be a basin for water—though that is not intended here. Its plural is aqwa', aqwa'in, and qi'an.

"The Safsaf" (صَفْصَفًا): It is the level, smooth earth, as if its parts are in a single row from every direction. It is also said to be land that has no vegetation.

From Ibn Abbas and Mujahid: Al-Qa' and al-Safsaf are given the same meaning, which is the level ground that has no vegetation.

"Qa'an" is in the accusative case as a circumstantial qualifier (hal) from the accusative pronoun, and it serves as a second direct object for "will leave" (yadharu), implying the meaning of "making" (tas'ir). "Safsafa" is either a second circumstantial qualifier or a substitute for the second direct object.