The Bible claims in a few places that whatever one prays for, god will answer that prayer. For example:
Matthew 21:21 Jesus answered and said unto them, Verily I say unto you, If ye have faith, and doubt not, ye shall not only do this which is done to the fig tree, but also if ye shall say unto this mountain, Be thou removed, and be thou cast into the sea; it shall be done. 22:22 And all things, whatsoever ye shall ask in prayer, believing, ye shall receive.
Or maybe this one (although one could argue that it's specifically talking about asking for god to show himself, but that's a bad argument to make since it's demonstrably not true):
Luke 11:9 “So I say to you, ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. 10 For everyone who asks receives, and he who seeks finds, and to him who knocks it will be opened. 11 If a son asks for bread[d] from any father among you, will he give him a stone? Or if he asks for a fish, will he give him a serpent instead of a fish? 12 Or if he asks for an egg, will he offer him a scorpion? 13 If you then, being evil, know how to give good gifts to your children, how much more will your heavenly Father give the Holy Spirit to those who ask Him!”
Or maybe this one does it for you:
Matthew 17:20 And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
For the Xian, these passages are troublesome for the obvious reason that prayer is rather ineffective. It is obviously not true that whatever one asks for, one receives. So, they have to conjure up reasons for why this is not so. I want to focus on one of those reasons, which is the idea that god only does what is according to his will, so the prayer must be in accord with god's will for it to be carried out.
And, in response to that, I have to say that it's a rather spectacularly bad argument.
First, the text does not give mention that what one prays for must be in accordance with god's will. Secondly, having to pray for things that god is going to do anyway completely negates the idea that prayer does anything at all. If the apologist is right, then prayer is completely ineffective, since one must first ask for something that was going to happen anyway, since it was part of god's will. The prayer has no effect since everything that happens was always a part of god's will or it wasn't. So, in trying to save the efficacy of prayer, the apologist has thrown it out the window and hoped that no one would notice. But, drastic measures must be taken when your beliefs do not agree with reality I suppose.