Once a diwan of the emperor came to meet Guru Har Gobind Sahib Ji. He was a Turk, arrogant because of his position. The Guru was absorbed in some thing, and so did not take notice of him. This indifference enraged the diwan. The idea crossed his mind that he should strike the Guru with his sword and sever his head from the body. The Guru who was all knowing, saw what was going on in the diwan's mind.
The emperor had commissioned him for a particular expedition, in which he had been defeated and forced to flee. As he thought of using the sword, the Guru looked towards him, and said, "You did not strike when you should have done it. But at a saint's place, where you are supposed to pay obeisance, you want to use your sword. Whence did you buy this advice? Go and return it to whoever sold it to you. This is useless." At this the diwan fell at the Guru's feet and said, "0 Guru, I made a grievous error. Forgive me for the ignoble thought. You are in reality, the "Sache Pathshah" (True Emperor). Nothing is hidden from you. You are rightly known as the True emperor. There is no exaggeration in this. I crave your forgiveness."
Guru ji remarked, "Listen, diwan, when you goto a saint, regard him as the image of the Creator. Do not take him to be a mere human being. If you approach him with wicked thoughts, your sword will clash with his far more powerful one, which will strike you dead, while your sword is in your hand. Such are the powers of the saints. They are not powerless. I forgive you. But do not forget the etiquette to be observed in the presence of masters. The more you respect them, the better it will be for you. The rest is up to you."
(Source : http://trilochankaur.blogspot.com)