Nedarim, Chapter 3, Mishnah 7. The Mishnah discusses someone who vowed not to benefit from "eilu she'hachamah ro'ah osam" - "those whom the sun sees," and teaches that this person is forbidden to benefit even from blind people.
Why should that be? Blind people do not see the sun.
Understanding the wording of the vow:
The Mishnah clarifies that the one who vowed did not say "those who see the sun," but rather "eilu she'hachamah ro'ah osam" - "those whom the sun sees." This means that he intended every person or object that the sun sees, and therefore blind people are included in the vow as well, since the sun does see them.
What did the one who vowed come to exclude?
With this wording he came to exclude people or things that the sun does not see, and these are they:
Fish in the sea - the sun does not see them.
Fetuses in their mothers' wombs - the sun does not see them.
These are not included in the vow, and the one who vowed is permitted to benefit from them.
In summary: One who vows against benefit from "those whom the sun sees" is forbidden even with regard to blind people, because the wording of his vow does not refer to a person's own sight but to the sun's seeing him; whereas fish in the sea and fetuses in their mothers' wombs, which the sun does not see, are not included in the vow.