The Mythology & Folklore Database
Here the woman helped the nix's wife deliver a child. To thank the midwife, the nixie told her that when the nix asked her how she should be paid, instead of money, she should ask for some of the sweepings.
Then the midwife bathed the new baby, and while doing so she heard the nix's other children -- there were five of them -- running around and asking their father, "Shall we pinch her? Shall we pinch her?" But the father told them not to.
When the midwife was finished the nix asked, "What shall I pay you?"
Following the wife's advice, she requested some of the sweepings from behind the door.
"God told you to say that," said the nix, giving her what she wanted. Then he took her back home, and when she looked at the sweepings, they had turned to pure gold.