Khastakhumār and Bībīnagār or Xasteh Xomār is an Afghan folktale. Both titles refer to tales about a poor maiden who marries a youth in snakeskin, loses him due to her breaking his trust, and goes after him at his mother's home, where she is forced to perform hard tasks for her.

The tale belongs to the international cycle of the Animal as Bridegroom or The Search for the Lost Husband, wherein a human princess marries a supernatural husband, loses him, and goes on a quest to find him. It is also distantly related to the Graeco-Roman myth of Cupid and Psyche, in that the heroine is forced to perform difficult tasks for a witch or her mother-in-law. According to scholarship, other variants are known in Afghanistan.

A version of the tale, titled Khastakhumār and Bībīnagār, was collected by professor Hafizullah Baghban in 1967, from a fifty-year-old farmer named Yar Muhammad. In this tale, an old kharkash ('thorn-seller', 'thorn-gatherer'), while gathering thorn bushes to sell, meets a black snake who asks for the man's youngest daughter's hand in marriage. He marries the maiden as a snake, but takes off his snake skin (his jild, a cover or disguise) and appears as a man in their bridal bed. The wife's two stepsisters, seeing the man and becoming jealous, convince her to ask about burning his jild skin. He questions his wife's interest in the matter, but answers her: it can be burned with garlic and onion skins. The stepsisters burn the jild, the man becomes a green pigeon and tells his wife she must wear down seven pairs of iron clothes, seven pairs of iron shoes and seven canes, all the way to the west, then she'll find him, and vanishes.

She begins her wanderings, and passes by a caravan of camels, a flock of sheep, a herd of cows, and a herd of donkeys - all belonging to her husband Khastakhumar. She arrives at a spring and asks for a drink of water, but a woman (concubine) says she is in a hurry and refuses her plight. Bibinagar curses the water the other is carrying to become pus and blood, which she gives to her master. The third time, the servant returns to fetch water, gives it to Bibinagar, and returns to her master. When the concubine pours down the water on her master's hands, a ring drops out of the jug that the master recognizes as Bibinagar's. Khastakhumar takes her in as a servant in his mother's house. His mother tries to get rid of her, by setting her to go to her sister to ask for khamīrturūsh (a sourdough ball used to prepare bread).

Before she goes, Khastakhumar intercepts her and teaches her to reach his aunt: she is to compliment a river of pus by saying it contains butter; compliment a river of blood by saying it contains juice; compliment a crooked tree; open his aunt's shut gate and shut her open one; and give the correct fodder to animals (bone to a dog and a straw to a donkey). The woman visits the witch, gets the khamirturush and escapes. The aunt commands the dog, the donkey, the gates, the tree and the rivers of pus and blood to stop Bibinagar, but the human woman leaves unscathed.

Next, Khastakhumar's mother forces Bibinagar to hold candles during Khastakhumar's marriage to his aunt's daughter: Khastakhumar's mother wraps cotton around her fingers and lights them up. Suffering their burning, Bibinagar cries out to Khastakhumar her fingers are burning, and he, in return, says his heart and soul are the ones that are burning. After his wedding to his cousin, Khastakhumar asks Bibinagar to boil water. His new wife takes the boiled water to the tushnuk (a sort of washroom), pours it on her head and dies.

The couple prepares to escape from Khastakhumar's family and takes with them a dozen needles, water in a sheepskin, a dozen juwāldūz (large sewing needles), salt and glass. As his family pursues them, the couple try to hinder the chase by throwing objects behind them: first the juwaldaz (which spread into large needles), then the needles, the salt, the glass (which turns the ground into glass) and finally the water to create a river between them. At the other side of the river, Khastakhumar's family asks how they crossed the stream. Bibinagar explains she crossed by pocketing some rocks and jumping. His family follows the false instructions and sink to the bottom. The couple wait until black blood foams at the river surface to confirm his family's demise. After they ascertain their victory, they go back to his father-in-law's house and remarry.

A second version of the tale was collected by American folklorist Margaret Mills from a woman named MZ, in the Dari language, titled Xasteh Xomār. In her version, a poor, old thorn-gatherer, while in the fields, lifts a stone and finds a hidden cache of flour. Thinking it is a divine blessing, he takes some and brings it home. When he returns, he sees a snake on top of the trapdoor, who explains it is the owner of the flour and demands one of the man's daughters in return. He tells the situation to his three daughters, but only the youngest accepts to be delivered to the snake.