Sa'id bin al-Musayyib (may Allah have mercy on him) narrates from Ma'mar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever hoards is a sinner." Someone said to Sa'id bin al-Musayyib (may Allah have mercy on him): But you also practise ihtikar (hoarding)? Sa'id bin al-Musayyib (may Allah have mercy on him) said: Ma'mar (may Allah be pleased with him), who narrates this hadith, also hoards himself.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11147