"I cannot speak for you, but I may speak for myself. If there is anything I know, anything that I am quite assured of beyond all question, it is that praying breath is never spent in vain. My own conversion is the result of long, affectionate, and earnest prayer. Parents prayed for me, God heard their cries, and here I am preaching the gospel. Since then I have adventured upon some things that were far beyond my capacity, but I have never failed because I cast myself upon the Lord. I have not hesitated to challenge our church with large ideas of what we might do for God, and we have accomplished all that we purposed. I have sought God's help in all my manifold undertakings, and though I cannot tell here the story of my private life in God's work, yet if it were written, it would be standing proof that there is a God that answers prayer. He has heard my prayers -not now and then- so many times that it has grown into a habit with me to spread my case before God with the absolute certainty that whatsoever I ask of God He will give to me. It is not now a perhaps or a possibility. I know that my Lord answers me, and it would be folly to doubt it. I am sure of this, for I have reaped it.
Still remember that prayer is always to be offered in submission to God's will. When we say that God hears prayer, we do not mean that He always gives us literally what we ask for. We do mean, however, that He gives us what is best for us and if He does not give us the mercy we ask for in silver, he bestows it upon us in gold. If He does not take away the thorn in the flesh, yet he says, 'My grace is sufficient for thee' (2 Cor. 12:9). We never offer up prayer without inserting the clause, either in spirit or in words, 'Nevertheless not as I will, but as thou will' (Mt. 26:39). We can only pray without an 'if' when we are quite sure that our will must be God's will, because God's will is fully our will."
-Charles Spurgeon, The Power of Prayer in a Believer's Life, pg. 53