Musnad Ahmad 27:840

'Abd al-Rahman narrated to us, Malik narrated to us, from Nafi', from Ibn 'Umar, "That the Prophet, peace and blessings of Allah be upon him, forbade *al-shighar*." Malik said: "And *al-shighar* is for a man to say: 'Marry me to your daughter, and I will marry you to my daughter.'"