Malik related to me that he had heard that Abdullah ibn Masudused to say, "If someone makes a loan, they should not stipulatebetter than it. Even if it is a handful of grass, it is usury."Malik said, "The generally agreed on way of doing things among usis that there is no harm in borrowing any animals with a setdescription and itemisation, and one must return the like of them.This is not done in the case of female slaves. It is feared about thatthat it will lead to making halal what is not halal, so it is notgood. The explanation of what is disapproved of in that, is that a manborrow a slave-girl and have intercourse with her as seems proper tohim. Then he returns her to her owner. That is not good and it is nothalal. The people of knowledge still forbid it and do not give anindulgence to any one in it."
USC-MSA web (English) reference: Book 31, Hadith 95
Arabic reference: Book 31, Hadith 1381