Wages (Kitab Al-Ijarah)
Dawud :: Book 23 : Hadith 3451
Narrated 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 (peace_be_upon_him) said: Two people must separate only by mutual consent.