Sunnan Abu Dawud Collection: ::Book Number 11:: Hadith # 2070
Narrated Mu'awiyah: AbdurRahman ibn Hurmuz al-A'raj said: Al-Abbas ibn Abdullah ibn al-Abbas married his daughter to AbdurRahman ibn al-Hakam, and AbdurRahman married his daughter to him. And they made this (exchange) their dower. Mu'awiyah wrote to Marwan commanding him to separate them. He wrote in his letter: This is the shighar which the Apostle of Allah (peace_be_upon_him) has forbidden.