2 Kings and 2 Chronicles describe Manasseh as one of the most idolatrous of the kings. Because of this Manasseh is taken captive by the Assyrians (2 Chronicles 33.11-13). There in Babylon Manasseh prays:
2 Chronicles 33:18-192 Chronicles doesn't give the words of the prayer, mentioning only that the prayer is recorded in "record of the seers."
The other events of Manasseh’s reign, including his prayer to his God and the words the seers spoke to him in the name of the Lord, the God of Israel, are written in the annals of the kings of Israel. His prayer and how God was moved by his entreaty, as well as all his sins and unfaithfulness, and the sites where he built high places and set up Asherah poles and idols before he humbled himself—all these are written in the records of the seers.
The words of the prayer are contained, however, in the Apocrypha. The Prayer of Manasseh (NRSV):
Prayer of ManassehThe words of this prayer are used by both Catholics and the Orthodox in their penitential confessions. The prayer is also used in the Book of Common Prayer--Canticle 14 in the Daily Office--as "A Song of Penitence" described there as being "especially suitable for Lent and on other penitential occasions."
Ascription of Praise
O Lord Almighty,
God of our ancestors,
of Abraham and Isaac and Jacob
and of their righteous offspring;
you who made heaven and earth
with all their order;
who shackled the sea by your word of command,
who confined the deep
and sealed it with your terrible and glorious name;
at whom all things shudder,
and tremble before your power,
for your glorious splendor cannot be borne,
and the wrath of your threat to sinners is unendurable;
yet immeasurable and unsearchable
is your promised mercy,
for you are the Lord Most High,
of great compassion, long-suffering, and very merciful,
and you relent at human suffering.
O Lord, according to your great goodness
you have promised repentance and forgiveness
to those who have sinned against you,
and in the multitude of your mercies
you have appointed repentance for sinners,
so that they may be saved.
Therefore you, O Lord, God of the righteous,
have not appointed repentance for the righteous,
for Abraham and Isaac and Jacob, who did not sin against you,
but you have appointed repentance for me, who am a sinner.
Confession of Sins
For the sins I have committed are more in number than the sand of the sea;
my transgressions are multiplied, O Lord, they are multiplied!
I am not worthy to look up and see the height of heaven
because of the multitude of my iniquities.
I am weighted down with many an iron fetter,
so that I am rejected because of my sins,
and I have no relief;
for I have provoked your wrath
and have done what is evil in your sight,
setting up abominations and multiplying offenses.
Supplication for Pardon
And now I bend the knee of my heart,
imploring you for your kindness.
I have sinned, O Lord, I have sinned,
and I acknowledge my transgressions.
I earnestly implore you,
forgive me, O Lord, forgive me!
Do not destroy me with my transgressions!
Do not be angry with me forever or store up evil for me;
do not condemn me to the depths of the earth.
For you, O Lord, are the God of those who repent,
and in me you will manifest your goodness;
for, unworthy as I am, you will save me according to your great mercy,
and I will praise you continually all the days of my life.
For all the host of heaven sings your praise,
and yours is the glory forever.
This is a prayer I've used many times.