The Bible does not mention Ash Wednesday or Lent, and the early New Testament Church did not observe these days. Here is how the BBC Religion page describes Ash Wednesday and Lent:
"Ash Wednesday is the beginning of Lent for Western Christian churches. It's a day of penitence to clean the soul before the Lent fast.
"Roman Catholic, Anglican, and some other churches hold special services at which worshippers are marked with ashes as a symbol of death and sorrow for sin…
"The Christian churches that observe Lent in the 21st century (and not all do significantly) use it as a time for prayer and penance. Only a small number of people today fast for the whole of Lent, although some maintain the practice on Ash Wednesday and Good Friday. It is more common these days for believers to surrender a particular vice such as favourite foods or smoking" (BBC).
Lent is counted differently by those of the Western Catholic tradition and those of the Eastern Orthodox tradition. "
The western church excludes Sundays (which is celebrated as the day of Christ's resurrection) whereas the eastern church includes them. The churches also start Lent on different days. Western churches start Lent on the 7th Wednesday before Easter Day (called Ash Wednesday). Eastern churches start Lent on the Monday of the 7th week before Easter and end it on the Friday 9 days before Easter. Eastern churches call this period the 'Great Lent'" (BBC).
Various biblical events and customs are referred to by those who celebrate these days. The Bible mentions people mourning in sackcloth and ashes. The Bible also talks about repentance and fasting, and the number 40 is prominent in various biblical events.
"The justification for the Lenten 40-day preparation for Easter is traditionally based on Jesus' 40-day wilderness fast before His temptation by Satan (Harper's Bible Dictionary, 'Lent'; Matthew 4:1-2; Mark 1:13). The problem with this explanation is that this incident is not connected in any way with Jesus' supposed observance of Easter. The 40-day pre-Easter practice of fasting and penance did not originate in the Bible" (The Good Friday—Easter Sunday Question).
Some have suggested that Lent may be connected to earlier, pagan holidays. In Ezekiel 8:14, the prophet in vision saw women weeping for the pagan god Tammuz. "It has been suggested by some scholars that the practice of 'weeping for Tammuz' was the actual origin of Lent, the Roman Catholic 40-day period of abstinence prior to Easter (starting after Mardi Gras, 'Fat Tuesday,' on Ash Wednesday). Consider that the name Easter itself is derived from Ishtar, the ancient Babylonian fertility goddess and Tammuz's mother". (See the Bible commentary on Ezekiel 8 for details.)
The Bible does teach the importance of fasting and self-examination, but it does not teach a 40-day period called Lent or an Ash Wednesday of putting ashes on the forehead. These customs appear to have pagan origins, and are not practiced by the United Church of God. We seek to follow the customs and practices of the early New Testament Church as described in the Bible. For more on the biblical religious festivals, such as the Passover and the Feast of Unleavened Bread in the spring, see God's Holy Day Plan: The Promise of Hope for All Mankind.