Al-Kahf 18:23

When the Quraysh posed the questions they had obtained from the Jewish scholars, the Prophet said, "I will answer you tomorrow," but did not say "God willing." According to the reports, revelation was then delayed for about fifteen days; the Meccans began to mock, and the delay weighed heavily on the Prophet. Then, together with the revelation containing the answers, the verses came down: "Never say of anything, 'I will surely do it tomorrow,' without adding, 'if God wills.'"

İbn İshâk, Sîre; Taberî, Câmiu'l-beyân

According to Ibn Ishaq, the Quraysh sent an-Nadr ibn al-Harith and Uqba ibn Abi Mu'ayt to the Jewish scholars of Yathrib (Medina) to test the Prophet. The scholars said: "Ask him about the young men of old who took refuge in a cave, about the traveller who reached the east and the west of the earth (Dhul-Qarnayn), and about the spirit; if he knows these, he is a prophet." In response to these questions the relevant sections of Surah al-Kahf were revealed; verses 9-26 relate the story of the young men of the cave.

İbn İshâk, Sîre; Taberî, Câmiu'l-beyân

Al-Kahf is Meccan. According to classical reports, it was revealed in response to questions the Quraysh put to the Prophet at the prompting of Jewish scholars in Medina, concerning the People of the Cave, Dhul-Qarnayn and the spirit. Through the stories of the People of the Cave, Moses and Khidr, and Dhul-Qarnayn, it offers guidance on faith, knowledge and power.

Klasik tefsir mukaddimeleri; İbn İshak ve esbâb-ı nüzul rivayetleri