Thomas Boston, Works, 6:420:
They are not true penitents who look on it as the work of some days or weeks, at the soul’s first conversion to God. A true penitent will aye [always] be repenting, as long as he is sinning. He sees that he is often falling into the mire, and therefore must be often washing; daily contracting new debt, therefore must be daily crying for forgiveness. And the more heinous his after miscarriages be, the longer he lies secure, his repentance will be the more bitter when he riseth up again.
Source: http://www.puritanboard.com/f25/true-penitent-will-always-repenting-85281/, Comment #1