It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) forbade shighar. The narrator says: I asked Nafi‘,“What is shighar?”He said: It is when a man marries his daughter to another man and himself marries that man's daughter, or similarly, when a man marries his sister to another man and himself marries that man's sister, while there is no dowry (mahr) in between.