This is the story about Khidr and Prophet Musa (Moses) a.s. taken from the Quran (verses 70-82, Al-Kahf).
70. He (Khidr) said, ‘ then if you follow me, ask me not about anything till I myself mention of it to you.’
71. So they both proceeded, till, when they embarked the ship, he scuttled it. Musa said, ‘have you scuttled it in order to drown its people? Verily, you have committed a thing Imr (a Munkar – evil, bad, dreadful thing)’
72. He (Khidr) said, ‘did i not tell you that you would not be able to have patience with me?’
73. Musa said, ‘call me no to account for what I forgot, and not hard upon me for my affair (with you)’
74. Then they both proceeded, till they met a boy, and he killed him. Musa said, ‘have you killed an innocent person who had killed none? Verily, you have committed a thing Nukr (a great Munkar – prohibited, evil, dreadful thing)
75. He said, ‘did I not tell you that you have no patience with me?’
76. Musa said, ‘if I ask you anything after this, keep me not in your company, you have received an excuse from.’
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 me and you, I will tell you the interpretation of (those) things over which you were unable to hold patience.’
79. ‘As for the ship, it belonged to Masakin (poor people) working in the sea. So i wished to make a defective damage in it, as there was a king behind them who seized every ship by force.’
80. ‘And for the boy, his parents were believers, and we feared lest he should oppress them by rebellion and disbelief.’
81. ‘So we intended that their Lord should change him for them for one better in righteouness and nearer to mercy.’
82. ‘And as for the wall, it belonged to two orphan boys in the town, and there was under it a treasure belonging to them, and their father was a righteous  man, and your Lord intended that they should attain their age of full strenght and take out their treasure as a mercy from your Lord. And I did them not of my own accord. That is the interpretation of those over which you could not hold patience.’
It is a nice story indeed, isn’t it? The most important is the lesson that we can learn from the story. As a human being, we can’t read one’s mind. Often, we don’t know the intentions that lie in one’s action, therefore, we should avoid being judgemental.