It is narrated from Hazrat Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: In Islam, there is no validity to exchange marriages (watte satta) in which no dowry (mahr) has been stipulated.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 12686
Hadith Gradingحکم دارالسلام:إسناده صحيح من جهة ثابت، وأما أبان بن أبى عياش فمتروك