get blood from a stone
US /ɡɛt blʌd frəm ə stoʊn/
UK /ɡɛt blʌd frəm ə stoʊn/

1.
to try to obtain something that is very difficult or impossible to get, especially money or information from someone who is unwilling to give it
:
•
Trying to make him pay back the loan is like trying to get blood from a stone.
•
Getting any information from the uncooperative witness was like trying to get blood from a stone.