“And Jesus answering saith unto them, Have faith in God.”
Mark 11:22

“…and shall not doubt in his heart…” Mark 11:23
When you’ve said exactly what you want TO THE CHALLENGE not God, then get ready to fight- the good fight of faith- because you could be granted many opportunities to doubt what you said would happen after you’re done talking, just like Jesus was:
“And Jesus answered and said unto it, No man eat fruit of thee hereafter for ever. And his disciples heard it. And they come to Jerusalem… And when even was come, he went out of the city. And in the morning, as they passed by, they saw the fig tree dried up from the roots.” Mark 11:14-15, 19-20
It took a day and night for the tree to wither, he passed that area on his way back from the temple at Jerusalem, and the tree was still standing, that would have been a good opportunity for him to doubt, but he didn’t doubt in his heart and because he is so kind, he teaches us the same: stick to what you’ve said, the Bible says:
“For let not that man think that he shall receive any thing of the Lord. A double minded man is unstable in all his ways.” James 1:7-8

Bible Reading Plan: Ezekiel 25 and Titus 1