This is a translation from the Soushenji, a collection of strange stories from around 300 C.E.
The Soushenji contains 464 texts in 20 rolls. This is text No. 395, in which a travelling scholar has an unusual encounter on the road, and ends up being granted an official title.
隴西辛道度者，遊學至雍州城四五里，比見一大宅，有青衣女子在門。度 詣門下求飧。女子入告秦女，女命召入。度趨入閣中，秦女於西榻而坐。 度稱姓名，敘起居，既畢，命東榻而坐。
即治飲饌。食訖，女謂度曰：「 我秦閔王女，出聘曹國，不幸無夫而亡。亡來已二十三年，獨居此宅，今 日君來，願為夫婦，經三宿。」
三日後，女即自言曰：「君是生人，我鬼 也，共君宿契，此會可三宵，不可久居，當有禍矣。然茲信宿，未悉綢繆 ，既已分飛，將何表信於郎？」即命取床後盒子開之，取金枕一枚，與度 為信。
度具以告。 妃聞，悲泣不能自勝，然向疑耳，乃遣人發冢啟柩視之，原葬悉在，唯不 見枕。解體看之，交情宛若。秦妃始信之。歎曰：「我女大聖，死經二十 三年，猶能與生人交往。此是我真女婿也。」
遂封度為駙馬都尉，賜金帛 車馬，令還本國。因此以來，後人名女婿為「駙馬；」今之國婿！亦為「 駙馬」矣。
Soushenji No. 395: The Escort Commandant
Xin Daodu, from Longxi Commandery, was travelling to further his education, and arrived at a place about four or five li away from Yangzhou. There he saw a large dwelling, with a woman wearing dark clothes standing at the door. Daodu went to the doorway to request a meal, and the woman went inside to tell Lady Qin, who ordered for him to be brought in. Daodu hastened inside the building, where Lady Qin was sitting on a couch near the west wall. Daodu announced his given name and family name, and after the formalities had been expressed, he was instructed to sit on a couch by the east wall.
A meal was prepared promptly. After eating, Lady Qin addressed Daodu: “I am the daughter of King Min of Qin, and I was betrothed to be married to [a member of the royal family from] the state of Cao, but unfortunately I perished without a husband. It’s now twenty-three years since I died, and since then I have lived alone in this house, but today you came here and it is my wish that we become husband and wife.”
After three days and three nights had passed, Lady Qin spoke of her thoughts: “You are a living person, yet I am a ghost. Because it was fated that we would sleep together, we have been able to spend these three nights with each other, but you cannot stay for long, otherwise misfortune would fall on us. These few nights have not been enough to learn about each other intimately, yet it is already time to separate. What can I give you, my husband, to express what has passed these last few nights?” She promptly had a box taken out from behind the bed, and opened it, taking out a golden pillow. This she gave to Daodu as a memento.
Once the tearful separation was over, she ordered the dark clothed woman to see Daodu to the gate. He had not taken more than a few steps when the residence could no longer be seen; there was only a burial mound. At that moment, Daodu rushed out of the tomb, but the golden pillow held against his chest had not changed in any strange way.
He made for the state of Qin, where he went to a market to try and sell the pillow. It just happened that he met an imperial concubine of Qin, who was travelling in the East. She saw that Daodu was selling a golden pillow, was suspicious, and asked to be given it to scrutinise. She questioned Daodu about the place he had got it from.
He told her everything. The concubine listened, was grief-stricken to tears and could not bear it. She was still doubtful of what she heard, and dispatched some men to exhume the grave and open the coffin to inspect it. Of the things that she [Lady Qin] was originally buried with, only the pillow could not be seen. When the body was disinterred and looked at, it did seem as if there had been intercourse. Only then did the imperial concubine of Qin believe it. She sighed, saying “My daughter is a great sage - even having been dead for twenty-three years, she can still interact with the living. This means that you are my real son-in-law.”
Accordingly, the title of Escort Commandant was bestowed upon Daodu. He was granted gold, silk, chariots and horses, and instructed to return to his own city. This is why, ever since then, people have called a son-in-law an “Escort Commandant”. Today’s royal son-in-law is likewise the Escort Commandant!