Who cares about the "first mention?" That's a fallacious argument.
In another instance, Tamar put ashes on her head after she was raped by her brother.
As a sign of penitance and mourning. When Catholics put that ashen mark on their head, it is a sign of repentance from their sins.
Matthew 6:2
Therefore when thou doest thine alms, do not sound a trumpet before thee,
as the hypocrites do in the synagogues and in the streets,
that they may have glory of men.
Verily I say unto you,
They have their reward.
Matthew 6:5
¶And when thou prayest,
thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men.
Verily I say unto you,
They have their reward.
Matthew 6:16 ¶Moreover when ye fast, be not, as the hypocrites,
of a sad countenance:
for they disfigure their faces,
that they may appear unto men to fast.
Verily I say unto you,
They have their reward.