Abu Dawud
Wages
Book Number: 017 / Hadith Number: 3451
Narated By AbuHurayrah : When AbuZur'ah made a business transaction with a man, he gave him the right of option. He then would tell him: Give me the right of option (to annul the bargain). He said: I heard AbuHurayrah say: The Apostle of Allah (pbuh) said: Two people must separate only by mutual consent.