Acts of Faith are common in morning prayers, and they should be said at any time in which we feel our faith is being tested or we are enduring temptation. An Act of Faith can be as simple as "My God, I believe in you," but the following is a traditional version which generations of Catholics memorized.
An Act of Faith
"O my God, I firmly believe that Thou art one God in three Divine Person, Father, Son, and Holy Spirit; I believe that Thy Divine Son became man, and died for our sins, and that He will come to judge the living and the dead. I believe these and all the truths which the Holy Catholic Church teaches, because Thou hast revealed them, who canst neither deceive nor be deceived. Amen."