Ibrahim bin Abd al-Rahman bin Abi Rabi'ah (may Allah have mercy on him) said that one day Sayyiduna Umar (may Allah be pleased with him) went to the market and noticed that people were hoarding with their surplus gold. Sayyiduna Umar (may Allah be pleased with him) said: No, and no delight of the eye! Allah Almighty brings provision to us, until when it arrives in our market, some people stand up and keep it back with their gold from the needy and the widows, that is, they hoard, until, when the one who brings goods to the market leaves, these hoarders sell as they please. But any merchant who brings goods in summer and winter and stops in our market, such a merchant is Umar's guest; let him sell his goods as Allah Almighty wills and hold them back as Allah Almighty wills.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11152