get blood out of from a stone

کندن مو از سر خرس

to make someone give or tell you something, when it is extremely difficult because of the character or mood of the person or organization you are dealing with
اصطلاح/ از آب کره نمی توان گرفت
Convincing fussy eaters to try new foods is like trying to get blood out of a stone

منابع

• https://dictionary.cambridge.org/dictionary/english/get-blood-out-of-from-a-stone