The Sunday of the Prodigal Son is the second Sunday of a three-week period prior to the commencement of Great Lent. On the previous Sunday, the services of the Church began to include hymns from the Triodion, a liturgical book that contains the services from the Sunday of the Publican and the Pharisee, the tenth before Pascha (Easter), through Great and Holy Saturday. As with the Sunday of the Publican and the Pharisee, the theme of this Sunday is repentance, and the focus on the parable of the Prodigal Son leads Orthodox Christians to contemplate the necessity of repentance in our relationship with our Heavenly Father.
Kontakion in Tone Three
When I disobeyed in ignorance Thy fatherly glory, I wasted in iniquities the riches that Thou gavest me. Wherefore, I cry to Thee with the voice of the prodigal son, saying, 'I have sinned before Thee, O compassionate Father, receive me repentant, and make me as one of Thy hired servants'.
Doxastikon in Tone Six
Loving Father, I have gone far from you, but do not forsake me, nor declare me unfitted for your Kingdom. The all-evil enemy has stripped me naked and taken all my wealth. I have squandered like the Profligate the graces given to my soul. But now I have arisen and returned, and I cry aloud to you, ‘Make me as one of your hired servants, You who for my sake stretched out Your spotless hands on the Cross, to snatch me from the fearsome beast and to clothe me once again in the first robe, for You alone art full of mercy'.
Source
See also this article titled "The Brother of the Prodigal Son".