Jesus promised impossible answers to believing prayer.

Mark 11:23-24 (ESV)

23 Truly, I say to you, whoever says to this mountain, ‘Be taken up and thrown into the sea,’ and does not doubt in his heart, but believes that what he says will come to pass, it will be done for him.

24 Therefore I tell you, whatever you ask in prayer, believe that you have received it, and it will be yours.

And Jesus also spent specific time teaching on perseverance in Prayer.

Luke 18:1-8 (ESV)

1 And he told them a parable to the effect that they ought always to pray and not lose heart.

2 He said, “In a certain city there was a judge who neither feared God nor respected man.

3 And there was a widow in that city who kept coming to him and saying, ‘Give me justice against my adversary.’

4 For a while he refused, but afterward he said to himself, ‘Though I neither fear God nor respect man,

5 yet because this widow keeps bothering me, I will give her justice, so that she will not beat me down by her continual coming.’”

6 And the Lord said, “Hear what the unrighteous judge says.

7 And will not God give justice to his elect, who cry to him day and night? Will he delay long over them?

8 I tell you, he will give justice to them speedily. Nevertheless, when the Son of Man comes, will he find faith on earth?”

The Little by Little Principle

Exodus 23:27-30 (ESV)

27 I will send my terror before you and will throw into confusion all the people against whom you shall come, and I will make all your enemies turn their backs to you.

28 And I will send hornets before you, which shall drive out the Hivites, the Canaanites, and the Hittites from before you.

29 I will not drive them out from before you in one year, lest the land become desolate and the wild beasts multiply against you.

30 Little by little I will drive them out from before you, until you have increased and possess the land.