seven ravens - wings of desire
"I am your sister; tell me if I can set you free." --- "Yes," said they, "thou canst still set us free, but it is very difficult." --- She said she would gladly do anything, no matter what it was. --- Then the ravens said: "For seven long years thou must not say one word on pain of death, and during that time must sew for each of us a shirt with the thread made from stinging nettles, which must not be ready either sooner or later, than the last day of the seven years."