"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 

We should go into His presence as a child goes to his father. We do it with reverence and godly fear, of course, but we should go with a childlike confidence and simplicity.

Give yourself to it,[the call to prayer] yield to it; and you will find not only that you have not been wasting time with respect to the matter with which you are dealing but that actually it has helped you greatly in that respect. You will experience an ease and a facility in understanding what you were reading, in thinking, in ordering matter for a sermon, in writing, in everything which is quite astonishing. Such a call to prayer must never be regarded as a distraction; always respond to it immediately, and thank God if it happens to you frequently.

Always respond to every impulse to pray. The impulse to pray may come when you are reading or when you are battling with a text. I would make an absolute law of this always obey such an impulse.

Prayer, in many ways, is the supreme expression of our faith in God.

Prayer

“There are many prayers that it would not be right to pray in public, but they are very dear to God’s ear in private.”—1894,
Sermon #2380