Volume 2 · Book 26 · Hadith 642
Narrated 'Imran: We performed Hajj-at-Tamattu' in the lifetime of Allah's Apostle and then the Quran was revealed (regarding Hajj-atTamattu') and somebody said what he wished (regarding Hajj-at-Tamattu') according his own opinion.
— Sahih Bukhari, Volume 2, Book 26: Pilgrimmage (Hajj), Hadith #642