Matthew 14:7-9 that he promised her with an oath to give her whatever she would ask:

Worsley⁽ⁱ⁾ ⁷ that he promised her with an oath to give her whatever she would ask: ⁸ and she, being before instructed by her mother, said, Give me here in a dish the head of John the baptist: ⁹ at which the king was distressed, but because of his oath, and of those who sat at table with him, he ordered it to be given her;