The question is how can you know when you need pray for a thing no longer? Do you really mean to say that you actually know the point at which you can cease asking God and you can begin to thank Him for the thing which you've asked for? I believe that you can. Maybe better read again the Bible definition of "faith." Faith is assurance of things hoped for, a belief in things not seen, to (oddly?) that when you come to that vital place where you have the assurance of the thing that you're hoping for. That you don't need to ask for it any longer. Now that's where you come to the place where you have the assurance. That's the experience of faith and it's through this faith that God speaks to us when we pray. Let's put it simply like a child could understand it.
First we know that God does speak to man through that inner voice called the still small voice. In the Bible we have many instances where the old saints heard the audible voice of God. We believe they did but God can also speak just as convincingly through the channel of your faculties. Faith is abundantly fundamentally a human faculty and God can use those faculties by the still small voice that He speaks of in His Word. But of course only a child of God can recognize that voice we've said that to you many times. That voice of God in the soul. You have to be born again, born into the family of God to hear that voice, but oh, what a joy, what a privilege to know that you're in such a family and have kinship with such a Father. You have to be born again of course.
Now there comes a question. How can you get from God, not by any power of your own, but by God's power, the assurance that you have been heard? The vital conviction that you are being answered. Yes, if you will pray sincerely for that which you feel would be pleasing to God and if you'll hold on with a fixed determination you'll come to the culminating conviction that you need pray for it no longer. I'm gonna repeat that. If you'll pray sincerely for that which you feel would be pleasing to God and you'll hold on wit a fixed determination you will come to the conviction that you need pray for it no longer. Why? Because the assurance has come into your heart, because you know God has heard you and you have that splendid assurance and you don't have to ask over and over again. In fact, you may feel that you just can't pray for them any longer because you have received the thing that you have asked for.
Now having meditated upon God's promises until there's born in your heart this assurance of things hoped for then you come humbly before the Lord with your desire and then you enter into the faith that sees the things you asked for. You believe as God's Word says that "everyone that asketh receiveth," you believe also the promise, "Whatsoever things ye desire when you pray believe you receive them and ye shall have them." Also, you believe 1Jn.5:14 and 15 that "This is the confidence that we have in Him that if we ask anything according to His will he hears us and if we know that He hears us whatsoever we ask we know that we have the petition that we desire of Him." You see, the same faith with which you began to pray gets stronger and stronger and assured faith comes that keeps you from praying any longer for your desire. There's such an assurance that God, that your Father has heard you so your faith has truly become appropriation and possession. But remember, faith is a gift of God and He gives the power to receive only as you're faithful in prayer and in the reading of His blessed Word.
I quoted to you sometime ago Joshua 7:10 where you have the story of Joshua lying on his face in prolonged desperate prayer for his people after their defeat at Ai and God speaks to him while he's lying there so long praying. He said, "Get thee up; wherefore liest thou upon thy face any longer?" God's telling Joshua that He had asked and now it was time to believe God, to quit asking, to get up and go about God's business, that God was taking care of it. Oh, so many times dearly Beloved, we ask and then we don't believe God, we don't receive it. I said one time I'd asked God so long for something and I was sitting there wondering about it. God spoke to my heart in that still small voice just as clearly, "Well, accept it! Accept it! Why don't you accept it?"
You know, the great point to remember here is that God's Word's true. You must believe it in spite of every contradiction. I don't mean contradiction in God's Word because I don't believe there are any but I'm talking about the contradictions of what people say and the circumstances and conditions about you. God's always faithful but the Devil who's the father of lies often deceives us into believing feelings and circumstances instead of God's Word. You know, we have that lesson the healing of the nobleman's son when he heard that Jesus came out of Judea into Galilee. You remember he went and besought Him that He would come down and heal his son for his son was at the point of death.
Now it's so often apt to be the case with us when prayer is offered for our deliverance we're unwilling to believe unless we feel some wonderful power our extraordinary sensation sometimes there are such things but many times there is not anything that we can see or feel or hear. But this nobleman didn't require anything. You remember that there was such urgency in the case. His son was near death and he said, "Come down and see my child 'ere he die." It was a faith which dared to press the cause so earnestly, so humbly and oh the Lord rewarded him. He said, "Go thy way. Thy son liveth." And you know that nobleman just turned about and went his way. There wasn't anything else that he could cling to except to believe Christ's Word. He couldn't immediately see his son to mark whether his condition was bettered or not, there was no visible means and he just had to believe that his son was recovered simply because Jesus had said so and His Word was true. That's just how it happened. Oh, that we could believe that Christ fulfilled His promises when we claim them in His name. Even before we can see any earthly circumstances to warrant to believe we have yet to learn how different faith is from sight. Oh, how we limit God by looking just at our five different faculties. We read that the man believed the Word that Jesus spoke to him and he went his way. He didn't look as to the way he felt or he saw or he heard. He just believed the Lord's Word. I wonder, would you have doubted the Lord's deliverance until you met the servant who bore the glad tidings of the Lord's (recovering?) You know from the Old Testament there's a statement in Psalm 78:41, "They turned back and tempted God, and limited the Holy One." Oh, this is just like a moan coming out of the depths of this soul because they have limited God. Clear and uncompromising is this denunciation, the sins of God's chosen people, the language of David here. They limited God. They were stubborn, rebellious and unbelieving. The words just came like a whiplash. They limited God. Oh, let's not limit God by asking to see this or to see that or that He might send us some sign, some wonderful token. Let's take Him at His Word, believe His precious Word, it will never fail you dearly Beloved. You can stand on the Word and having done all stand, for God is on the throne. Prayer does change and will change things for you if you'll only believe. Amen.