From Sahih Bukhari (Hadith 5116):
Narrated 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
Reference: Bukhari 5116