Well, you read the scripture for yourself. If someone is a believer, but holds a grudge not willing to forgive a fellow believer, then Jesus says of that person, neither heavenly Father forgive you. In fact in the context, the man was originally forgiven all his debt, but when he would not have compassion on his fellow believer, his sins were reinstated.
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Because of this, the kingdom of heaven is like a king who wanted to settle accounts with his servants.
24As he began the settlements, a debtor was brought to him owing ten thousand talents.
25Since the man was unable to pay, the master ordered that he be sold to pay his debt, along with his wife and children and everything he owned.
26Then the servant fell on his knees before him. ‘Have patience with me,’ he begged, ‘and I will pay back everything.’
27His master had compassion on him, forgave his debt, and released him.
28But when that servant went out, he found one of his fellow servants who owed him a hundred denarii.
g He grabbed him and began to choke him, saying, ‘Pay back what you owe me!’
29So his fellow servant fell down and begged him, ‘Have patience with me, and I will pay you back.’
30But he refused. Instead, he went and had the man thrown into prison until he could pay his debt.
31When his fellow servants saw what had happened, they were greatly distressed, and they went and recounted all of this to their master.
32Then the master summoned him and declared, ‘You wicked servant! I forgave all your debt because you begged me.
33Shouldn’t you have had mercy on your fellow servant, just as I had on you?’
34In anger his master turned him over to the jailers to be tortured, until he should repay all that he owed.
35That is how My heavenly Father will treat each of you unless you forgive your brother from your heart.”