Muwatta Imam Malik Book of Business Transactions, Hadith 95

Malik related to me that he had heard that Abdullah ibn Masud used to say, "If someone makes a loan, they should not stipulate better than it. Even if it is a handful of grass, it is usury."
Malik said, "The generally agreed on way of doing things among us is that there is no harm in borrowing any animals with a set description and itemisation, and one must return the like of them. This is not done in the case of female slaves. It is feared about that that it will lead to making halal what is not halal, so it is not good. The explanation of what is disapproved of in that, is that a man borrow a slave-girl and have intercourse with her as seems proper to him. Then he returns her to her owner. That is not good and it is not halal. The people of knowledge still forbid it and do not give an indulgence to any one in it."

وَحَدَّثَنِي مَالِكٌ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، كَانَ يَقُولُ مَنْ أَسْلَفَ سَلَفًا فَلاَ يَشْتَرِطْ أَفْضَلَ مِنْهُ وَإِنْ كَانَتْ قَبْضَةً مِنْ عَلَفٍ فَهُوَ رِبًا . قَالَ مَالِكٌ الأَمْرُ الْمُجْتَمَعُ عَلَيْهِ عِنْدَنَا أَنَّ مَنِ اسْتَسْلَفَ شَيْئًا مِنَ الْحَيَوَانِ بِصِفَةٍ وَتَحْلِيَةٍ مَعْلُومَةٍ فَإِنَّهُ لاَ بَأْسَ بِذَلِكَ وَعَلَيْهِ أَنْ يَرُدَّ مِثْلَهُ إِلاَّ مَا كَانَ مِنَ الْوَلاَئِدِ فَإِنَّهُ يُخَافُ فِي ذَلِكَ الذَّرِيعَةُ إِلَى إِحْلاَلِ مَا لاَ يَحِلُّ فَلاَ يَصْلُحُ وَتَفْسِيرُ مَا كُرِهَ مِنْ ذَلِكَ أَنْ يَسْتَسْلِفَ الرَّجُلُ الْجَارِيَةَ فَيُصِيبُهَا مَا بَدَا لَهُ ثُمَّ يَرُدُّهَا إِلَى صَاحِبِهَا بِعَيْنِهَا فَذَلِكَ لاَ يَصْلُحُ وَلاَ يَحِلُّ وَلَمْ يَزَلْ أَهْلُ الْعِلْمِ يَنْهَوْنَ عَنْهُ وَلاَ يُرَخِّصُونَ فِيهِ لأَحَدٍ .