Muwatta Imam Malik Book of Business Transactions, Hadith 50

Yahya related to me from Malik that he had heard that Sulayman ibn Yasar said, "The fodder of the donkeys of Saad ibn Abi Waqqas ran out and so he told his slave to take some of the family's wheat and buy barley with it, and to only take a like quantity."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ سُلَيْمَانَ بْنَ يَسَارٍ، قَالَ فَنِيَ عَلَفُ حِمَارِ سَعْدِ بْنِ أَبِي وَقَّاصٍ فَقَالَ لِغُلاَمِهِ خُذْ مِنْ حِنْطَةِ أَهْلِكَ فَابْتَعْ بِهَا شَعِيرًا وَلاَ تَأْخُذْ إِلاَّ مِثْلَهُ .