Musnad Ahmad 8:129

Yahya ibn Sa'id narrated to us, Sulayman—meaning al-Taymi—informed us, Ghunaym narrated to me, he said: I asked Sa'd ibn Abi Waqqas about *al-mut'ah* (temporary marriage). He said: "We practiced it while this one was a disbeliever in the Throne," meaning Mu'awiyah.