But that would have taken place in Gen 16.
But it didn't!
Genesis 16:1-2; Sarai, Abram's wife, had borne him no children, she had a slave girl named Hagar and said to Abram "go and sleep with Hagar, perhaps I can build a family through her."
Genesis 16:3 "Abram agreed to what Sarai said."
He did NOT say, "the Lord has promised me that I will have many descendants and an heir who is my own flesh and blood", Genesis 15:4-5. We need to be patient and believe the Lord's promise." Sarai's reasoning was "The Lord has not given me children; if my slave girl becomes pregnant, her children will be mine - and Abram will still be their father."
You need to ask yourself when did God say it would be through Sarah the seed would come? It was in Gen 17: 15
Abram had TWICE received a promise that he would have as many descendants as the stars in the sky. Sarai was his wife. They had clearly being trying for a family for some years because she said "the Lord has prevented me from having children." It's very likely that Abram would have thought "if I am to have many descendants, that means Sarai will be pregnant soon."
But maybe the Lord did have to spell it out to him because he thought "it doesn't matter who I get pregnant as long as I have a child."
But we're talking about how he used his FAITH in regard to Sarah and her condition.
Seems pretty clear that his faith wavered at that point.
He agreed to sleep with a slave girl. When Hagar became pregnant, Sarai got jealous and said to Abram "it's your fault I'm suffering. I gave you Hagar, she got pregnant and now she despises me. May the Lord judge between you and me.", Genesis 16:5. And he replied "she's your slave girl; do whatever you think is best." Hagar ran away because Sarai mistreated her - Abram had washed his hands of this. She was only encouraged to return to Sarai after an angel of the Lord gave her a promise of her own.
Abram was 86 when Ishmael was born - he had to wait another 14 years for Isaac.
As I recall, the reason I mentioned Abraham was to show that sometimes God made promises to people and they believed, but they did not immediately receive what had been promised.
So I see what you're trying to say. You're trying to say if God gave you something it's just going to fall on you like ripe cherries off of a tree. You don't have to believe or do anything.
If God says he is going to give something he gives it.
We need to believe and accept it, but he does not say "there are conditions to you receiving this blessing/salvation/healing; you have to DO this first". God blesses because he chooses to bless. Of course we don't have to earn it - we deserve nothing from God and cannot do anything to earn, or deserve, his blessings.
That's not the way we see in scripture.
Isn't it?
How many times did Jesus day to someone "I will heal/bless you but you have to do something first"? He healed some people without asking about their faith. He healed the man at the pool of Bethesda who believed a superstition about being the first in the pool after an angel had disturbed the waters a little. He raised Jairus' daughter and Lazarus, who were dead.
He calmed the storm on the lake, and rebuked their disciples for their lack of faith.
He feed a crowd of more than 5,000, who had not even asked for food, never mind done anything to earn it.
He died for sinners, who did not believe or do anything (except sin). And he gives eternal life to all who receive it, Romans 6:23.
Even with Israel God had given them the promised land but they had to go into the land and possess it through their faith and actions of belief.
If God gives a gift, we need to receive it - yes; same in Romans 6:23.
But that is not the same as saying that he will only heal us if we believe; as though faith is a condition for the healing.
Otherwise, those who showed faith, by praying and asking their Father for healing, would
always receive it, while people with no faith would remain unhealed. Yet there are non Christians who have been healed, and some lovely, sincere Christians who remain ill/paralysed/have died.
You even said yourself that a Minister who was close to God and praying for someone's healing was told, "no".