"I live in the spirit of prayer; I pray as I walk, when I lie down and when I rise, and the answers are always coming." George Mueller 

"If your faith does not make you pray, have nothing to do with it: get rid of it, and God help thee to begin again." C. H. Spurgeon

"The spirit of prayer is more precious than treasures of gold and silver." John Bunyan

"In all your prayers forget not to thank the Lord for his mercies." John Bunyan 

"If weak in prayer, we are weak everywhere." — Leonard Ravenhill

"None can believe how powerful prayer is, and what it is able to effect, but those who have learned it by experience. It is a great matter when in extreme need to take hold on prayer. I know, whenever I have prayed earnestly, that I have been amply heard, and have obtained more than I prayed for. God indeed sometimes delayed, but at last He came." 
Martin Luther

"A sinning man stops praying, a praying man stops sinning." Leonard Ravenhill

"He that is never on his knees on earth, shall never stand upon his feet in heaven." C. H. Spurgeon