You cannot make a single hair white or black

Jesus said to his disciples:
"You have heard that it was said to your ancestors,
Do not take a false oath,
but make good to the Lord all that you vow.
But I say to you, do not swear at all;
not by heaven, for it is God's throne;
nor by the earth, for it is his footstool;
nor by Jerusalem, for it is the city of the great King.
Do not swear by your head,
for you cannot make a single hair white or black.
Let your 'Yes' mean 'Yes,' and your 'No' mean 'No.'
Anything more is from the Evil One."
(Mt 5:33-37)