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Surah 18. Al-Kahf
Ayah 77 - 78
77 فَٱنطَلَقَا حَتَّىٰٓ إِذَآ أَتَيَآ أَهْلَ قَرْيَةٍ ٱسْتَطْعَمَآ أَهْلَهَا فَأَبَوْا۟ أَن يُضَيِّفُوهُمَا فَوَجَدَا فِيهَا جِدَارًا يُرِيدُ أَن يَنقَضَّ فَأَقَامَهُۥ ۖ قَالَ لَوْ شِئْتَ لَتَّخَذْتَ عَلَيْهِ أَجْرًا
78 قَالَ هَـٰذَا فِرَاقُ بَيْنِى وَبَيْنِكَ ۚ سَأُنَبِّئُكَ بِتَأْوِيلِ مَا لَمْ تَسْتَطِع عَّلَيْهِ صَبْرًا
77. Then they both proceeded till when they came to the people of a town, they asked them for food, but they refused to entertain them. Then they found therein a wall about to collapse and he set it up straight. (Musa) said: "If you had wished, surely you could have taken wages for it!'' 78. He said: "This is the parting between you and I, I will tell you the interpretation of (those) things over which you were not able to be patient.''
(they both proceeded) after the first two instances,
(till when they came to the people of a town,) Ibn Jarir narrated from Ibn Sirin that this was Al-Aylah. According to the Hadith;
(When they came there, the people of the town were mean.) i.e., miserly
(they asked them for food, but they refused to entertain them. Then they found therein a wall about to collapse and he (Khidr) set it up straight.) means, he fixed it so it was standing upright properly. We have already seen in the Hadith quoted above that he set it up with his own hands, supporting it until it was standing straight again, which is something extraordinary. At this point Musa said to him:
(If you had wished, surely you could have taken wages for it!) meaning, because they did not entertain us as guests, you should not have worked for them for free.
(He said: "This is the parting between you and I) meaning, because you said after the boy was killed that if you asked me anything after that, you would not accompany me any further. So this is the parting of the ways between me and you.
(I will tell you the interpretation) meaning explanation,
(of (those) things over which you were not able to be patient.)