There are many scriptures on this subject. Listed below are the ones that most ministered to me when I realized I needed to forgive my mom. They were my motivators and instructors.
For if you forgive other people when they sin against you, your heavenly Father will also forgive you. Matthew 6:14 NIV
…and forgive us our debts, as we forgive our debtors. Matthew 6:12 KJV
Then Peter came to him and asked, “Lord, how often should I forgive someone who sins against me? Seven times?” “No, not seven times,” Jesus replied, “but seventy times seven!” Matthew 18:21-22 NLT
And when you stand praying, if you hold anything against anyone, forgive them, so that your Father in heaven may forgive you your sins. Mark 11:25 NIV
Be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you. Ephesians 4:32 NASB
A few years later when I again struggled to forgive other issues, I knew the scriptures above but the Lord used the following to help me.
Since God chose you to be the holy people He loves, you must clothe yourselves with tenderhearted mercy, kindness, humility, gentleness, and patience. Make allowance for each other’s faults, and forgive anyone who offends you. Remember, the Lord forgave you, so you must forgive others. Colossians 3:12-13 NLT
But I say, love your enemies! Pray for those who persecute you! In that way, you will be acting as true children of your Father in heaven. For He gives His sunlight to both the evil and the good, and He sends rain on the just and the unjust alike. Matthew 4:44-45 NLT
Accept one another then, just as Christ accepted you, in order to bring praise to God. Romans 15:7 NLT
A man’s discretion makes him slow to anger, and it is his glory to overlook a transgression. Proverbs 19:11 NASB
And on the days when injustice seemed to rule and there was no mercy on the other person’s part, the Lord reminded me that He has the final say in EVERY matter; that He would hold accountable those who were merciless.
There will be no mercy for those who have not shown mercy to others. But if you have been merciful, God will be merciful when He judges you. James 2:13 NLT