Matt. 6:7 - Jesus teaches, "do not heap up empty phrases" in prayer. Protestants use this verse to criticize various Catholic forms of prayer which repeat phrases, such as litanies and the Rosary. But Jesus' focus in this instruction is on the "vain," and not on the "repetition."
Matt. 26:44 - for example, Jesus prayed a third time in the garden of Gethsemane, saying the exact same words again. It is not the repetition that is the issue. It's the vanity. God looks into our heart, not solely at our words.
Luke 18:13 - the tax collector kept beating his breast and praying "God be merciful to me, a sinner." This repetitive prayer was pleasing to God because it was offered with a sincere and repentant heart.
Acts 10:2,4 - Cornelius prayed constantly to the Lord and his prayers ascended as a memorial before God.
Rom. 1:9 - Paul says that he always mentions the Romans in his prayers without ceasing.
Rom. 12:12 - Paul commands us to be constant in prayer. God looks at what is in our heart, not necessarily how we choose our words.
1 Thess. 5:17 - Paul commands us to pray constantly. Good repetition is different than vain repetition.
Rev. 4:8 - the angels pray day and night without cessation the same words "Holy, Holy, Holy is the Lord God Almighty." This is repetitious prayer that is pleasing to God.
Psalm 136 - in this Psalm, the phrase "For His steadfast love endures forever" is more repetitious than any Catholic prayer, and it is God's divine Word.
Dan. 3:35-66 - the phrase "Bless the Lord" is similarly offered repeatedly, and mirrors Catholic litanies.