Biblical Basis for Ash Wednesday?

One of my readers asked me what the Biblical basis for Ash Wednesday is. I answer:

I don't see any biblical basis either for Ash Wednesday or for Lent generally (Ash Wednesday marking the start of Lent). In fact, the practice of traipsing around throughout the day with ashes on one's forehead is contrary to Jesus' teaching:

Matthew 6:17-18

17 But thou, when thou fastest, anoint thine head, and wash thy face; 18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.

-TurretinFan