Sayyiduna Ibn Umar (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) forbade shighar. Imam Malik (may Allah have mercy on him) said: And shighar is that a person marries off his daughter or sister on the condition that the other person also marries off his daughter or sister to him without a dowry. Imam Darimi (may Allah have mercy on him) was asked: Will such a marriage be valid? He replied: I do not like it.