كتاب البيوع
Read the English translation first, with the original Arabic directly underneath.
Narrated Ibn `Umar:
Allah's Messenger (ﷺ) said, "The seller and the buyer have the option of canceling or confirming the deal unless they separate, or one of them says to the other, 'Choose (i.e. decide to cancel or confirm the bargain now)." Perhaps he said, 'Or if it is an optional sale.' " Ibn `Umar, Shuraih, Ash-Shu`bi, Tawus, Ata, and Ibn Abu Mulaika agree upon this judgment.
الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا، أَوْ يَقُولُ أَحَدُهُمَا لِصَاحِبِهِ اخْتَرْ