Tafsir of Al-Isra 17:109

The act of falling upon the faces is repeated due to the difference in the cause; for the first was to magnify the affair of Allah the Exalted or to give thanks for the fulfillment of the promise, while the second is due to the impact of the Qur’anic exhortations upon them.

The prepositional phrase (to the chins) relates either to the verb preceding it or to an elided term that serves as a circumstantial qualifier (hal) for what precedes or follows it—meaning: "prostrating." The sentence "they weep" is also a circumstantial qualifier, meaning: "weeping from the fear of Allah the Exalted." Since weeping arises from the fear that originates in reflection—which is ever-renewing—the verbal sentence was employed to signify renewal.

Many reports have come down in praise of weeping out of His fear. Al-Tirmidhi extracted from al-Nadr ibn Sa‘d that the Messenger of Allah, peace and blessings be upon him, said: "If a single servant were to weep in a nation, Allah the Exalted would save that nation from the Fire through the weeping of that servant. Every deed has a weight and a reward, except for the tear, for it extinguishes oceans of Fire. No eye has ever welled up with its water out of the fear of Allah the Exalted, but that Allah forbade its body from the Fire; and if it overflows onto his cheek, neither darkness nor humiliation shall overcome his face."

He also extracted from Ibn ‘Abbas who said: I heard the Messenger of Allah, peace and blessings be upon him, saying: "Two eyes shall not be touched by the Fire: an eye that wept out of the fear of Allah the Exalted, and an eye that spent the night standing guard in the cause of Allah the Exalted."

He, along with al-Nasa'i and Muslim, extracted from Abu Hurayrah that the Messenger of Allah, peace and blessings be upon him, said: "A man who wept out of the fear of Allah the Exalted will not enter the Fire until the milk returns to the udder; nor will the dust of the cause of Allah the Exalted and the smoke of Hell ever gather on a servant." (Al-Nasa'i added: "in his nostrils," and Muslim added: "ever.")

This should be the condition of the scholars. Ibn Jarir, Ibn al-Mundhir, and others extracted from ‘Abd al-A‘la al-Taymi that he said: "Whoever is given knowledge that does not make him weep is deserving of having been given knowledge that does not benefit him, for Allah the Exalted described the people of knowledge, saying: 'And they fall upon their faces weeping.'"

"And it increases them"—meaning the Qur’an, through their hearing of it—"in humility," because it adds to their knowledge and certainty regarding the command of Allah the Exalted, beyond the proofs they already possessed.