GOD'S WORD® Translation
I can guarantee this truth: This is what will be done for someone who doesn't doubt but believes what he says will happen: He can say to this mountain, 'Be uprooted and thrown into the sea,' and it will be done for him.

American Standard Version
Verily I say unto you, Whosoever shall say unto this mountain, Be thou taken up and cast into the sea; and shall not doubt in his heart, but shall believe that what he saith cometh to pass; he shall have it.

Berean Study Bible
“Truly I tell you that if anyone says to this mountain, ‘Be lifted up and thrown into the sea,’ and has no doubt in his heart but believes that it will happen, it will be done for him.

Douay-Rheims Bible
Amen I say to you, that whosoever shall say to this mountain, Be thou removed and be cast into the sea, and shall not stagger in his heart, but believe, that whatsoever he saith shall be done; it shall be done unto him.

English Revised Version
Verily I say unto you, Whosoever shall say unto this mountain, Be thou taken up and cast into the sea; and shall not doubt in his heart, but shall believe that what he saith cometh to pass; he shall have it.

King James Bible
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.

World English Bible
For most certainly I tell you, whoever may tell this mountain, 'Be taken up and cast into the sea,' and doesn't doubt in his heart, but believes that what he says is happening; he shall have whatever he says.

Young's Literal Translation
for verily I say to you, that whoever may say to this mount, Be taken up, and be cast into the sea, and may not doubt in his heart, but may believe that the things that he saith do come to pass, it shall be to him whatever he may say.

Mark 11:23 Additional Translations ...