All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If removing fat from the stomach and transferring it to another part of the body, like the buttocks, requires a surgical operation, then this is not permissible for two reasons:
1- It is forbidden to undergo a surgical operation for the purpose of beautification except in case of aberrant deformation or to replace a loss [in a part of the body] caused by a road accident or any other accident.
2- This kind of operation requires one to disclose the 'Awrah (parts of the body that must be covered in Islam) and even one’s private parts, and it is not permissible to voluntarily expose one's 'Awrah except between spouses.