Almighty and everlasting God, who hath compassion upon all men, and hateth nothing that thou hast made, passing over the sins of men because of their repentance; who also succourest them that labour in necessity, vouchsafe to bless and sanctify these ashes, which thou hast ordered that, after the manner of the Ninevites, we should bear upon our heads, for the sake of humility, and of our holy religion, and for the cleansing away of our offences ; and grant that by calling on thy holy name, all those who have thus borne ashes on their heads may be thought worthy to receive from thee pardon of all their sins, and so to-day commence the observation of their holy fasts, that on the day of Resurrection they may be found worthy to approach the holy Paschal feast with minds purified, and hereafter to share in glory everlasting. Through etc.
Here is the entire service in English
Gregorian Sacramentary: dies cinerum (day of ashes) 8th century or earlier.
In the beginning, Lent started on Quadragesima -- the Fourth Sunday before Easter. Originally, ashes were imposed on penitents as a sign, at least as early as the 6th century, and there was no direct connection with Easter Lent. In the 10th century, Wednesday, a normal fast day, was observed as a day for penitents before Lent, and ashes were imposed on the heads of those who came to church that day for the ceremony. Finally Urban II specified the use of ashes on the Wednesday before Lent. Later the day was called, "Ash Wednesday". In the 12th century the tradition of using the ashes from branches of palms, saved from the previous year's Palm Sunday observance, were directed for use.
We read in the books both in the Old Law and in the New that the men who repented of their sins bestrewed themselves with ashes and clothed their bodies with sackcloth. Now let us do this little at the beginning of our Lent that we strew ashes upon our heads to signify that we ought to repent of our sins during the Lenten fast.
Aelfric [c. 1005-1020]
--Released by Primus Pilus
Legio Christi-Ecclesia Militans
"Let us therefore follow after the things which make for peace, and things wherewith one may edify another" [St. Paul's Epistle to the Romans 14:19]
* ORDO CENTURIONUM * IN HOC SIGNO VINCES * TIME DEUM ET OPERARE IUSTITIAM