CHAPTER: Regarding Shighar Marriages..
Ibn Umar said “The Messenger of Allah صلی اللہ علیہ وسلم prohibited shighar marriage. Musaddad added in his version “I said to Nafi “What is shighar?” (It means that) a man marries the daughter of another man and gives his own daughter to him in marriage without fixing dower; and a man marries the sister of another man and gives him his sister in marriage without fixing dower.
Abdur Rahman ibn Hurmuz al-Araj said: Al-Abbas ibn Abdullah ibn al-Abbas married his daughter to Abdur Rahman ibn al-Hakam, and Abdur Rahman married his daughter to him. And they made this (exchange) their dower. Muawiyah wrote to Marwan commanding him to separate them. He wrote in his letter: This is the shighar which the Messenger of Allah صلی اللہ علیہ وسلم has forbidden.