Bava Batra 151 - Will in Anticipation of Death
The sister of Rav Dimi bar Yosef had an orchard. Whenever her health would worsen, she would transfer it to him as a sickbed gift, and when she would recover, she would retract the gift.
One time, she felt weak and sent a message to him, "Come, acquire the orchard from me," but Rav Dimi did not come. She sent a message "Come, acquire it in any way you wish." Rav Dimi went and asked her to give him only a portion, and to perform a formal act of acquisition, hoping to make the gift irreversible . She did all that, then recovered and reneged on the gift, but Rav Dimi did not want to return it.
She went to Rav Nachman, who ruled that since she said "Woe, I am dying!" she made the gift only under the impression that she was dying and thus may still retract.
Art: Johannes Vermeer - Girl with a Red Hat