Sahih Bukhari Volume 7, Book 62, Hadith Number 51.

Narrated By Abu Jamra : I heard Ibn Abbas (giving a verdict) when he was asked about the Mut’a with the women, and he permitted it (Nikah-al-Mut’a). On that a freed slave of his said to him, “That is only when it is very badly needed and women are scarce.” On that, Ibn ‘Abbas said, “Yes.”