Here are some verses that can be Help full in doing DAWAH to the christians. They are regarding Interest and what the Bible had to say.
Exodus 22:25
"If you lend money to one of my people among you who is needy, do not be like a moneylender; charge him no interest.
Leviticus 25:36
Do not take interest of any kind from him, but fear your God, so that your countryman may continue to live among you.
Leviticus 25:37
You must not lend him money at interest or sell him food at a profit.
Deuteronomy 23:19
Do not charge your brother interest, whether on money or food or anything else that may earn interest.
Exodus 22:25
"If you lend money to one of my people among you who is needy, do not be like a moneylender; charge him no interest.
Leviticus 25:36
Do not take interest of any kind from him, but fear your God, so that your countryman may continue to live among you.
Leviticus 25:37
You must not lend him money at interest or sell him food at a profit.
Deuteronomy 23:19
Do not charge your brother interest, whether on money or food or anything else that may earn interest.