Does the Bible speak of losing faith?

Where does the Bible refer to losing faith? What is Hebrews 6:4-6 speaking of? There is a conversation among friends wanting Scripture reference that there is danger of losing faith, others believe once saved, always saved. What Scriptures talk about the subject?

Some Bible verses that speak of losing faith are:  Luke 8:13; 1 Corinthians 10:12; Galatians 5:4; 1 Timothy 1:19-20; and, 2 Peter 3:17.

The Greek of Hebrews 6:4-6 can be translated to describe a person who has committed the sin against the Holy Spirit (Matthew 12:31-32) or a person who has fallen from faith but can still be brought back to faith.  You can see those options in the text and the footnote of the NIV, for example.  Regardless of which option in translating we take, it is obvious from that section of Scripture—and elsewhere—that “once saved, always saved” has no scriptural basis.