The famous Sufi master Rumi, who is very well known to most of you, has a story in which he talks of a man who goes to the house of a friend, and he knocks on the door, and a voice answers, "Who's there?"
我们非常熟知的，著名的苏非派大师鲁米， 讲述过一个故事，一个人走到他朋友的房前， 他敲门， 一个声音问他，“谁在哪儿？”