《太平广记·卷一·神仙一》
据说老子要向西出关去，守关的令尹名叫喜，知道老子不是一般人，就向他问道。
或云：老子欲西度关，关令尹喜知其非常人也，从之问道。
It is said that Laozi was about to leave the pass westward, and the magistrate guarding the pass named Xi knew that Laozi was not an ordinary person, so he asked him.