Question: Is it true that the Prophet (sws) married the widow of his adopted son. If so why and is this allowed? Please explain. 
    Answer: Adoption is of two types:
    a) To adopt a child during his suckling age so that he can drink the milk of the mother who has adopted him. In this case, the child will be her foster-son and there will be no difference between him or her and the mother’s real children in any manner. He or she will possess the same rights in all affairs (eg inheritance) as the real children possess. This relation is as strong as the real or blood relation. 
    b) To adopt a child when he is past his suckling age. In this case, he of course will not be the son of the parents who have adopted him in the legal sense. He will be called by the name of his previous father. The parents who have adopted him can of course address him as ‘son’. The child will consequently not inherit their wealth after them, unless of course they make a will in his favour. This type of relation is not recognized as strong as the real or blood relation. 
    In Arabia, both types of adoption prevailed. However, the two were not differentiated between. In spite of the fact that the second type did not establish a real relation , it carried the same restrictions as the first one in which a real relationship is established between the two. The need arose to reform this evil social practice and the Almighty chose none other than the Prophet (sws) Himself to do away with this custom considering its deep roots in the society.