James 1: 5-8 NIV 

If any of you lacks wisdom, you should ask God, who gives generously to all without finding fault, and it will be given to you. But when you ask, you must believe and not doubt, because the one who doubts is like a wave of the sea, blown and tossed by the wind. That person should not expect to receive anything from the Lord. Such a person is double-minded and unstable in all they do.

Mark 11:20-24 NIV

In the morning, as they went along, they saw the fig tree withered from the roots. Peter remembered and said to Jesus, “Rabbi, look! The fig tree you cursed has withered!” “Have faith in God,” Jesus answered. “Truly I tell you, if anyone says to this mountain, ‘Go, throw yourself into the sea,’ and does not doubt in their heart but believes that what they say will happen, it will be done for them. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours.

Romans 4: 19-25 NIV

Without weakening in his faith, he faced the fact that his body was as good as dead since he was about a hundred years old and that Sarah’s womb was also dead. Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised. This is why “it was credited to him as righteousness.” The words “it was credited to him” were written not for him alone, but also for us, to whom God will credit righteousness—for us who believe in him who raised Jesus our Lord from the dead. He was delivered over to death for our sins and was raised to life for our justification.