Muhammad bin Ishaq mentioned the reason why this Surah was revealed. He said that an old man from among the people of Egypt who came to them some forty-odd years ago told him, from `Ikrimah that Ibn `Abbas said: "The Quraysh sent An-Nadr bin Al-Harith and `Uqbah bin Abi Mu`it to the Jewish rabbis in Al-Madinah, and told them: `Ask them (the rabbis) about Muhammad, and describe him to them, and tell them what he is saying. They are the people of the first Book, and they have more knowledge of the Prophets than we do.' So they set out and when they reached Al-Madinah, they asked the Jewish rabbis about the Messenger of Allah . They described him to them and told them some of what he had said. They said, `You are the people of the Tawrah and we have come to you so that you can tell us about this companion of ours.' They (the rabbis) said, `Ask him about three things which we will tell you to ask, and if he answers them then he is a Prophet who has been sent (by Allah); if he does not, then he is saying things that are not true, in which case how you will deal with him will be up to you. Ask him about some young men in ancient times, what was their story For theirs is a strange and wondrous tale. Ask him about a man who travelled a great deal and reached the east and the west of the earth. What was his story And ask him about the Ruh (soul or spirit) -- what is it If he tells you about these things, then he is a Prophet, so follow him, but if he does not tell you, then he is a man who is making things up, so deal with him as you see fit.' So An-Nadr and `Uqbah left and came back to the Quraysh, and said: `O people of Quraysh, we have come to you with a decisive solution which will put an end to the problem between you and Muhammad. The Jewish rabbis told us to ask him about some matters,' and they told the Quraysh what they were. Then they came to the Messenger of Allah and said, `O Muhammad, tell us,' and they asked him about the things they had been told to ask. The Messenger of Allah said,

«أُخْبِرُكُمْ غَدًا عَمَّا سَأَلْتُمْ عَنْه»

(I will tell you tomorrow about what you have asked me.) but he did not say `If Allah wills.' So they went away, and the Messenger of Allah stayed for fifteen days without any revelation from Allah concerning that, and Jibril, peace be upon him, did not come to him either. The people of Makkah started to doubt him, and said, `Muhammad promised to tell us the next day, and now fifteen days have gone by and he has not told us anything in response to the questions we asked.' The Messenger of Allah felt sad because of the delay in revelation, and was grieved by what the people of Makkah were saying about him. Then Jibril came to him from Allah with the Surah about the companions of Al-Kahf, which also contained a rebuke for feeling sad about the idolators. The Surah also told him about the things they had asked him about, the young men and the traveler. The question about the Ruh was answered in the Ayah;

﴿وَيَسْـَلُونَكَ عَنِ الرُّوحِ قُلِ الرُّوحُ﴾

(And they ask you concerning the Ruh (the spirit); say: "The Ruh...'') ﴿17:85﴾.

﴿فَلَعَلَّكَ بَـخِعٌ نَّفْسَكَ عَلَى ءَاثَـرِهِمْ إِن لَّمْ يُؤْمِنُواْ بِهَـذَا الْحَدِيثِ أَسَفاً - إِنَّا جَعَلْنَا مَا عَلَى الاٌّرْضِ زِينَةً لَّهَا لِنَبْلُوَهُمْ أَيُّهُم أَحْسَنُ عَمَلاً - وَإِنَّا لَجَاعِلُونَ مَا عَلَيْهَا صَعِيداً جُرُزاً ﴾

(6. Perhaps, you would kill yourself in grief, over their footsteps, because they believe not in this narration.) (7. Verily, we have made that which is on earth an adornment for it, in order that We may test which of them are best in deeds.) (8. And verily, We shall make all that is on it bare, dry soil.)