Al-Kahf - 18:77

فَانطَلَقَا حَتَّى إِذَا أَتَيَا أَهْلَ قَرْيَةٍ اسْتَطْعَمَا أَهْلَهَا فَأَبَوْا أَن يُضَيِّفُوهُمَا فَوَجَدَا فِيهَا جِدَارًا يُرِيدُ أَنْ يَنقَضَّ فَأَقَامَهُ قَالَ لَوْ شِئْتَ لَاتَّخَذْتَ عَلَيْهِ أَجْرًا
[18:77]
So they went on until when they came to the people of a town, they asked them for food, but they refused to entertain them as guests. Then they found in it a wall which was on the point of falling, so he put it into a right state. (Musa) said: If you had pleased, you might certainly have taken a recompense for it.
Then they proceeded: until, when they came to the inhabitants of a town, they asked them for food, but they refused them hospitality. They found there a wall on the point of falling down, but he set it up straight. (Moses) said: "If thou hadst wished, surely thou couldst have exacted some recompense for it!"
So they twain journeyed on till, when they came unto the folk of a certain township, they asked its folk for food, but they refused to make them guests. And they found therein a wall upon the point of falling into ruin, and he repaired it. (Moses) said: If thou hadst wished, thou couldst have taken payment for it.