Kulayb bin Wa'il says: I said to Ibn Umar (may Allah be pleased with them both): "I had some dirhams to collect from a certain man. I went to him to collect them, and he said: 'I have nothing at present, but write it down against food until the harvest.'" Ibn Umar (may Allah be pleased with them both) said: "That is not proper."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11120