One of the mightiest men of prayer of the last generation was George Mueller of Bristol, England, who in the last sixty years of his life (he lived to be ninety-two or ninety-three) obtained the English equivalent of $7,200,000.00 by prayer. But George Mueller never prayed for a thing just because he wanted it, or even just because he felt it was greatly needed for God's work. When it was laid upon George Mueller's heart to pray for anything, he would search the Scriptures to find if there was some promise that covered the case. Sometimes he would search the scriptures for days before he presented his petition to God. And then when he found the promise, with his open Bible before him, and his finger upon that promise, he would plead that promise, and so he received what he asked. He always prayed with an open Bible before him.
-R. A. Torrey on George Müeller