"It is not enough for the believer to begin to pray, nor to pray correctly; nor is it enough to continue for a time to pray. We must patiently, believingly continue in prayer until we obtain an answer. Further, we have not only to continue in prayer until the end, but we have also to believe that God does hear us and will answer our prayers. Most frequently we fail in not continuing in prayer until the blessing is obtained, and in not expecting the blessing. Those who are disciples of the Lord Jesus should labor with all their might in the work of God as if everything depended upon their own endeavors. Yet, having done so, they should not in the least trust in their labor and efforts, nor in the means that they use for the spread of the truth, but in God alone; and they should with all earnestness seek the blessing of God in persevering, patient, and believing prayer. Here is the great secret of success, my Christian reader. Work with all your might, but never trust in your work. Pray with all your might for the blessing in God, but work at the same time with all diligence, with all patience, with all perseverance. Pray, then, and work. Work and pray. And still again pray, and then work. And so on, all the days of your life. The result will surely be abundant blessing. Whether you see much fruit or little fruit, such kind of service will be blessed."

George Mueller on Expectant Prayer