Malik reported,

A man wanted to buy food from another man on credit, so the man who intended to sell him the food took him to the market and began showing him the heaps of grain, saying to him, "Which of these would you like me to buy for you?"The buyer said, "Are you selling me something you do not possess?"So the two of them went to Abdullah bin Umar and told him what had happened.Abdullah bin Umar said to the buyer, "Do not buy from him what he does not possess."And he said to the seller, "Do not sell what you do not possess."

وحدثني

عن مالك، أنه بلغه

أن رجلا أراد أن يبتاع طعاما من رجل إلى أجل، فذهب به الرجل الذي يريد أن يبيعه الطعام إلى السوق، فجعل يريه الصبر، ويقول له: من أيها تحب أن أبتاع لك، فقال المبتاع: أتبيعني ما ليس عندك؟ فأتيا عبد الله بن عمر فذكرا ذلك له، فقال عبد الله بن عمر للمبتاع: لا تبتع منه ما ليس عنده، وقال للبائع: لا تبع ما ليس عندك.