For thus saith the Lord God of Israel, The barrel of meal shall not waste, neither shall the cruse of oil fail, until the day that the Lord sendeth rain upon the earth. (1 Kings 17:14)
The request was accompanied by a promise. She was told of the blessings that her giving would bring. God made clear to her that if she gave to the prophet, He would return to her far more than she had given. She met the test and was richly rewarded.