Muwatta Imam Malik Book of Business Transactions, Hadith 94

Yahya related to me from Malik from Nafi that he heard Abdullah ibn Umar say, "If someone lends something, let the only condition be that it is repaid."

وَحَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، أَنَّهُ سَمِعَ عَبْدَ اللَّهِ بْنَ عُمَرَ، يَقُولُ مَنْ أَسْلَفَ سَلَفًا فَلاَ يَشْتَرِطْ إِلاَّ قَضَاءَهُ .