Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "When two men transact a sale, they have the option as long as they have not separated, or their sale is itself (concluded) with an option." Sayyiduna Umar or Ibn Umar (may Allah be pleased with them) used to proclaim: The sale is either a binding deal (safqah) or (a sale with) an option.
It was also narrated through Mutarrif bin Tarif, once from al-Sha'bi from Umar, and once from Ata bin Abi Rabah from Umar (may Allah be pleased with him): "The sale is either a binding deal or an option." Both of these, along with the first, are weak because they are munqati' (broken chains). If it is authentic, then what is meant by it — and Allah knows best — is a sale in which it is stipulated that the option is cut off, so they have no option after the deal; whereas in a sale in which cutting off the option is not stipulated, they both have the option as long as they have not separated. Many scholars held the report from Umar to be weak, held that stipulating the cutting off of the option is not permissible in a sale, and held that what is meant by "a sale with an option" is either giving the choice after the sale, or a sale with a stipulated three-day option, so that their option does not end by separating because of the stipulation. The correct view — and Allah knows best — is that he meant giving the choice after the sale, except that Nafi' sometimes expressed it as "a sale with an option" and sometimes explained it; and what makes this clear is the following report.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10454