What is the ruling on donating a portion of the liver to a mother afflicted with a malignant tumor and early-stage cirrhosis, and what is the reward for such an act if it is permissible?

It is permissible to donate a part of the liver to one's mother, provided two conditions are met: that the benefit to the mother is proven through examinations, and that the donation does not cause harm to the donor. This is because the liver regenerates after a part of it is donated, making it similar to blood donation, which is agreed upon to be permissible.