I found this bio of George Muller on the Desiring God website. It is very detailed and very good at pointing out what his worldview was and how that affected his prayers and his actions.
A few quotes:
According to my judgement the most important point to be attended to is this: above all things see to it that your souls are happy in the Lord. Other things may press upon you, the Lord’s work may even have urgent claims upon your attention, but I deliberately repeat, it is of supreme and paramount importance that you should seek above all things to have your souls truly happy in God Himself! Day by day seek to make this the most important business of your life. This has been my firm and settled condition for the last five and thirty years. For the first four years after my conversion I knew not its vast importance, but now after much experience I specially commend this point to the notice of my younger brethren and sisters in Christ: the secret of all true effectual service is joy in God, having experimental acquaintance and fellowship with God Himself.
And this one:
Therefore, if it is really good for me, my darling wife will be raised up again; sick as she is. God will restore her again. But if she is not restored again, then it would not be a good thing for me. And so my heart was at rest. I was satisfied with God. And all this springs, as I have often said before, from taking God at his word, believing what he says.