Sayyiduna Hakim bin Hizam (may Allah be pleased with him) said: I said to the Messenger of Allah (peace and blessings be upon him): O Messenger of Allah! A man comes to me (and asks): Sell me this thing; then should I go to the trouble of procuring it from the market for him? He (peace and blessings be upon him) said: "Do not sell what is not with you."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10705