"Bibles read without prayer; sermons heard without prayer; marriages contracted without prayer; journeys undertaken without prayer; residences chosen without prayer; friendships formed without prayer; the daily act of private prayer itself hurried over, or gone through without heart: these are the kind of downward steps by which many a Christian descends to a condition of spiritual palsy, or reaches the point where God allows him to have a tremendous fall. This is the process which forms the lingering Lots, the unstable Samsons, the wife-idolizing Solomons, the inconsistent Asas, the pliable Jehoshaphats, the over-careful Marthas, of whom so many are to be found in the church of Christ. Often the simple history of such cases is this: they became careless about private prayer. You may be very sure men fall in private long before they fall in public." -- J.C. Ryle, A Call to Prayer, page 18
I am reading the booklet by Ryle. But if you want a free copy of the thing, get the pdf here.