Musnad Abu Ya'la al-Mawsili 245:17

Ibrahim ibn Sa'id narrated to us, Ya'qub ibn Ibrahim ibn Sa'd narrated to us, he said: My father narrated to me, from Muhammad ibn Ishaq, he said: 'Abd al-Rahman al-A'raj ibn Hurmuz narrated to me, that al-'Abbas ibn 'Abd Allah ibn al-'Abbas gave his daughter in marriage to 'Abd al-Rahman ibn al-Hakam, and 'Abd al-Rahman gave his daughter in marriage to him, and they had made them [the marriages] as a dowry for each other. Mu'awiyah ibn Abi Sufyan, while he was Caliph, wrote to Marwan and ordered him to separate them. He said in his letter: "This is *al-shighar* (exchange marriage), and the Messenger of Allah, peace and blessings of Allah be upon him, has forbidden it."