Sahih Bukhari Volume 2, Book 26, Hadith Number 710.

Narated By ‘Asim : I asked Anas bin Malik: “Did you use to dislike to perform Tawaf between Safa and Marwa?” He said, “Yes, as it was of the ceremonies of the days of the Pre-lslamic period of ignorance, till Allah revealed: ‘Verily! (The two mountains) As-Safa and Al-Marwa are among the symbols of Allah. It is therefore no sin for him who performs the pilgrimage to the Ka’ba, or performs ‘Umra, to perform Tawaf between them.'” (2.158)