What did Prophet Muhammad (peace be upon him) say about the practice of Shighar and Mut'a?
      Narrated 'Abdullah:                          Nafi narrated to me that 'Abdullah said that Allah's Apostle forbade      the Shighar. I asked Nafi', "What is the Shighar?" He said, "It is to      marry the daughter of a man and marry one's daughter to that man (at      the same time) without Mahr (in both cases); or to marry the sister of     a man and marry one's own sister to that man without Mahr." Some      people said, "If one, by a trick, marries on the basis of Shighar, the     marriage is valid but its condition is illegal." The same scholar said     regarding Al-Mut'a, "The marriage is invalid and its condition is      illegal." Some others said, "The Mut'a and the Shighar are permissible     but the condition is illegal."