get blood from / out of a stone / turnip

/ɡɛt blˈʌd fɹɒm ˌaʊtəv ɐ stˈəʊn tˈɜːnɪp/

/ɡɛt blˈʌd fɹʌm ˌaʊɾəv ɐ stˈoʊn tˈɜːnɪp/

to try to do something that is very unlikely to accomplish

Examples

1. Getting her to read is like getting blood from a stone.

2. The goods have to be returned to their rightful owner and getting money back from the seller is like getting blood out of a stone.

3. And it was like getting blood out of a stone.