Rav Zutra bar Tuvya's mother wrote her property to her son before marrying Rav Zevid (to hide her assets). He divorced her. Rav Zutra bar Tuvya did not want to return the assets to his mother, he claimed that since the wedding went through the assets became his.What kind of son doesn't give his mother her money back no matter what the legal technicality is?
The Gemara relates another similar story:
Rav Dimi bar Yosef's sister had a small orchard. Whenever she got sick, she would give it to him. When she recovered, she would retract.Again, what kind of brother doesn't return the money to his sister when she makes it clear that her original gift was only because she thought she was dying and now she wants the money back? Even if technically he is entitled to the money it is certainly not the moral thing to do.
Once, she got sick and called him to come to acquire it. He sent a message 'I am not interested.' She sent to him 'come and acquire it however you want (i.e. in a way that will not allow me to retract).'
He left part for her, and made a Kinyan on the rest. She recovered and retracted, and came in front of Rav Nachman. He called Rav Dimi to come.
Rav Dimi saw no need to come. Since she kept part, it was like a healthy person's gift, and he acquired!