Mark 11:23-26New International Version (NIV).
23 “Truly[a] 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. 24Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours. 25 And when you stand praying, if you hold anything against anyone, forgive them, so that your Father in heaven may forgive you your sins.”  [b]
Matthew 6:15New International Version (NIV)
15 But if you do not forgive others their sins, your Father will not forgive your sins.