This ancient prayer is prescribed for the Canonical Hours of the weekdays of Great Lent. It is attributed to St Ephraim the Syrian (AD 306-373) and is an excellent summary of how we should strive to purify ourselves during Great Lent not just through fasting and abstinence but also through a genuine change of heart.
The translation below is from the All-Night Vigil Sluzhebnik, printed with the Blessing of His Eminence Archbishop Laurus of Syracuse and Holy Trinity 1990.
O Lord and Master of my life,
A spirit of idleness, despondency, ambition,
and idle talking give me not.
But rather a spirit of chastity, humble-mindedness,
Patience, and love bestow upon me Thy servant.
Yea, O Lord King, grant me to see my own failings
And not condemn my brother;
for blessed art Thou unto the ages of ages.
Then twelve bows from the waist, saying at each bow:
O God, cleanse me a sinner.
And again, without division, the same prayer entirely to the end,
And one prostration.