Tafsir of Al-Kahf 18:68

This is an announcement that he, upon him be peace, handles hidden matters whose purposes are outwardly objectionable. A righteous man—especially one who possesses a revealed Law—cannot restrain himself from being repulsed when witnessing them. It is as if he [Al-Khidr] also knew of the intensity of Moses, upon him be peace, and the extent of his zeal, which had previously led him to seize the head of his brother and drag him.

The word khubran (knowledge) is in the accusative case as a tamyiz (specifier) derived from the subject; the original phrasing being "that about which your knowledge has not encompassed." It is from khabara (to know), of the trilateral verb forms nasara and ‘alima, meaning "to know." It is also permitted that it be an infinitive (masdar), governed by tuhit (you encompass), as it matches it in meaning, for "encompassing" is commonly used to mean "knowledge"—as if it were said: "You have not experienced it as knowledge." Al-Hasan and Ibn Hurmuz read khubran with a damma on the letter ba (as khubran).

The Imam and others have used this verse as evidence that the istita'ah (capacity/ability) does not exist before the act. They argued: If capacity were present before the occurrence of the act, then the capacity for patience would have existed before the occurrence of patience; thus, denying it would be a lie, which is false. Therefore, it is established that it does not exist before the act.

Al-Jubba’i replied that the intent behind this statement is that patience is burdensome for you, just as it is said in common usage that so-and-so "cannot" see or sit with such-and-such a person when that is heavy upon him. The Imam countered this by noting that it is a deviation from the apparent meaning and supported the [original] line of reasoning with further corroboration.

The truth is that the deduction from this verse regarding the aforementioned matter is not apparent, because the intent is nothing more than the negation of patience by negating that upon which it depends—namely, the capacity—and this holds true whether that capacity exists beforehand or is simultaneous. Furthermore, the claim that capacity exists before the act is not exclusive to the Mu'tazila; rather, it is understood from the words of Shaykh Ibrahim al-Kurani that it is also the position of the Salaf. The investigation of that belongs in its own place.