Reasonable doubt is if you really don't know
Mark 11:23
23 For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.
The cure for unbelief is to find out what God said, and make a decision to believe it
Romans 10:17
So then faith cometh by hearing, and hearing by the word of God.
5 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.
Doubt means to hesitate, to contend, to differ, to stagger, to waver
John 15:7
7 If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you.
Stars, Sand, and changed his name to Abraham
10 And when he had called unto him his twelve disciples, he gave them power against unclean spirits, to cast them out, and to heal all manner of sickness and all manner of disease.
45 My heart is inditing a good matter: I speak of the things which I have made touching the king: my tongue is the pen of a ready writer.