Tafsir of Al-Kahf 18:81

(So we intended that their Lord should substitute for them [a child] better than him): That is, He will provide them with a son in his place who is better than him.

(In purity/righteousness [zakatan]): Ibn Abbas said: "Meaning, in religion." This is an interpretation based on implication. Many others said: "Meaning, purity from sins and reprehensible morals." The mention of the title of Lordship (Rububiyyah) and its attribution to them contains what is not hidden of the indication toward the intention of goodness reaching them.

(And closer in affection [rahman]): Meaning, in mercy (rahmah). Ru'bah ibn al-Ajjaj said: "O You who send down mercy (al-raham) upon Idris, and send down the curse upon Iblis." Both are verbal nouns (masdar), similar to kathr and kathrah. The intent is closer in mercy toward them and in righteousness (birr) to them. Abu Hayyan considered this to be the most likely view. Perhaps the reason for this is the frequent usage of the verbal noun in the form associated with the doer (fa'il), along with the consistency here with the preceding verbal noun.

Ibn Abi Shaybah, Ibn al-Mundhir, and Ibn Abi Hatim recorded from 'Atiyyah that the meaning is: "They are more merciful toward them than the boy was." Perhaps the intention, according to this, is that the child is more beloved to them than that boy, either due to the superiority of his character, his creation, or both together. This meaning is closer to being the ta'sis (foundational meaning) than the first meaning, based on the interpretation of the preceding conjunctive, as you have heard. However, that interpretation is supported by what Ibn al-Mundhir and Ibn Abi Hatim recorded from Ibn Abbas: "They were substituted with a girl who gave birth to a prophet." Al-Tha'labi said: "She reached [the time of] Yunus ibn Matta, and a prophet from among the prophets married her, and she gave birth to a prophet through whose hands God guided a nation from among the nations." In a narration by Ibn al-Mundhir from Yusuf ibn 'Umar, it is said she gave birth to two prophets. In another narration from Ibn Abbas and Ja'far al-Sadiq (may Allah be pleased with both of them), she gave birth to seventy prophets. Ibn Atiyyah considered this far-fetched, saying: "The abundance of prophets (peace be upon them) is not known except among the Children of Israel, and this woman was not from them." There is clear scrutiny in this [objection]. The perspective of the supporting evidence is that a girl, according to custom, loves her parents, shows mercy to them, is affectionate toward them, and is more righteous to them than a boy.

It is said: He substituted for them a believing boy like them. The accusative case of the two verbal nouns is due to specification (tamyiz), and the operative factor ('amil) is what precedes each of the comparative superlatives (af'al al-tafdil). The subtlety in the initial ambiguity followed by the subsequent clarification is not hidden; this is why it was not said: "So we intended that their Lord should substitute for them one who is azka (purer) and arham (more merciful) than him." Furthermore, the word zakatan contains a level of praise that azka does not, as becomes clear through honest reflection.

Abu Hayyan mentioned that af'al (comparative) is not for comparison here, because there is no zakah (purity) or rahmah (mercy) in that boy. This was refuted by stating that he was apparently pure from sins by action if he was young, and apparently so if he was an adult; thus, Musa (peace be upon him) said: "A pure soul (nafs zakiyah)," and this [verse] is in contrast to that. So, being better than zakah is for one who is pure in the present and the outcome, according to both the apparent and the hidden state. Even if one were to concede [that he wasn't], the assumed participation [in the quality] is sufficient for the validity of the comparison, and his statement "and no mercy" is a statement without evidence.

Al-Khafaji said: "The correct answer here is to suffice with the assumed participation, because Al-Khidr (peace be upon him) was knowledgeable of the hidden reality, so he knew that there was no zakah or rahmah in him [the boy]; thus, his statement that 'there is no evidence for it' has no standing." You know that mercy, according to the second interpretation, is something whose negation is not correct, because it is the pivot of fear—so understand. The apparent [meaning] is that the Fa (particle) is for derivation, so it indicates that the fear was the cause for the aforementioned intention. It is understood from the derivation of the killing—though he did not derive it himself, despite it being the intended meaning—the interpretation rests upon the obviousness of its understanding from this sentence in the most subtle way. In it is an indication of rejecting what Musa’s (peace be upon him) speech implied, that his killing was injustice and corruption in the land.

• Nafi’, Abu 'Amr, Abu Ja'far, Shaybah, Humayd, al-A'mash, and Ibn Jarir recited (yubdilahuma) with emphasis (shaddah).
• Ibn 'Amir, Abu Ja'far in one narration, Ya'qub, and Abu Hatim recited (ruhman) with a damma on the Ha.
• Ibn Abbas (may Allah be pleased with them both) recited (rahaman) with a fatha on the Ra and a kasra on the Ha.