Who asked God to send a famine that killed thousands of people?

Nephi (the son of Helaman Jr.)

Nephi did cry unto the Lord, saying: O Lord, do not suffer that this people shall be destroyed by the sword; but O Lord, rather let there be a famine in the land. ... And so it was done, according to the words of Nephi. And there was a great famine upon the land. ... They did perish by thousands. Helaman 11:3-6