Hadith 513430
Chapter 31: Business Transactions - كتاب البيوع
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، أَنَّهُ أَخْبَرَهُ أَنَّ عَبْدَ الرَّحْمَنِ بْنَ الأَسْوَدِ بْنِ عَبْدِ يَغُوثَ فَنِيَ عَلَفُ دَابَّتِهِ فَقَالَ لِغُلاَمِهِ خُذْ مِنْ حِنْطَةِ أَهْلِكَ طَعَامًا فَابْتَعْ بِهَا شَعِيرًا وَلاَ تَأْخُذْ إِلاَّ مِثْلَهُ .
Yahya related to me from Malik from Nafi that Sulayman ibn Yasar told him that one time the fodder of the animals of Abd ar-Rahman ibn al-Aswad ibn Abd Yaghuth was finished so he said to his slave, "Take some of your family's wheat as food and buy with it barley, and take only a like quantity.' "
Reference Muwatta Malik 513430
USC-MSA web (English) reference : Book 31, Hadith 51