Muwatta Imam Malik Book of Business Transactions, Hadith 43

Yahya related to me from Malik from Nafi that Hakim ibn Hizam traded in food for people as Umar ibn al-Khattab had ordered him to do. Hakim re-sold the food before he had taken delivery of it. That reached Umar ibn al-Khattab and he revoked the sale and said, "Do not sell food which you have purchased until you take delivery of it."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، . أَنَّ حَكِيمَ بْنَ حِزَامٍ، ابْتَاعَ طَعَامًا أَمَرَ بِهِ عُمَرُ بْنُ الْخَطَّابِ لِلنَّاسِ فَبَاعَ حَكِيمٌ الطَّعَامَ قَبْلَ أَنْ يَسْتَوْفِيَهُ فَبَلَغَ ذَلِكَ عُمَرَ بْنَ الْخَطَّابِ فَرَدَّهُ عَلَيْهِ وَقَالَ لاَ تَبِعْ طَعَامًا ابْتَعْتَهُ حَتَّى تَسْتَوْفِيَهُ .