Sunan Ibn Majah, Chapter: The Chapters on Wills

"The Prophet (saw) addressed them when he was on his camel. His camel was chewing its cud and its saliva was dripping between my shoulders. He said: 'Allah (swt) has allocated for each heir his share of the inheritance, so it is not permissible (to make) a bequest for an heir. The child belong to the bed and the adulterer gets the stone. Whoever claims to belong to someone other than his father, or (a freed slave) who claims that his Wala is for other than his Mawali, upon him will be the curse of Allah, the angels and all the people, and no charge nor equitable exchange will be accepted from him." Or he said: "No equitable exchange nor change." Hasan