Buying back a gift from the one to whom it was given
Question

                A man gave a car to his brother as a gift, then the one to whom it was given wanted to sell the car. Can the one who gave him the car buy it or is it not permissible for him to buy it?.
Praise be to Allah.
    It is not permissible for the giver to buy the thing he gave 
    to his brother. It was narrated that ‘Umar (may Allaah be pleased with him) 
    said: I gave a horse to someone (to ride in jihad) for the sake of Allaah, 
    and its owner neglected it. I thought that he would sell it cheaply, so I 
    asked the Messenger of Allaah  (peace and blessings of Allaah be upon 
    him) about that, and he said: “Do not buy it, even if he gives it to you for 
    a dirham, for the one who takes back his charity is like a dog that goes 
    back to its vomit.” 

    And Allaah is the Source of strength.