It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) forbade exchange marriages (watte satta) in which, without specifying a dowry, the exchange of relations itself is considered as the dowry.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 9666