"Clement notes that Peter so repented that, all his life after, every night when he heard the cock crow, would fall upon his knees, and weeping bitterly, would beg pardon for his sin. Ah! Souls, you can easily sin as the saints, but can you repent with the saints? Many can sin with David and Peter, who cannot repent with David and Peter, and so must perish forever." - Spurgeon's Sermon Notes
Further recommended reading & listening:
The Best of The Daily Spurgeon
The Forgotten Spurgeon, by Iain Murray
A Defense of Calvinism - by Charles Spurgeon