In Mazhab Hanbali, if a couple did zina, they cannot marry at all and should be separated at once. Is this true?
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
According to Imam Ahmad it is unlawful for a man to marry a woman with whom he committed Zina before both of them repent to Allah.
Now, if they marry before repenting, the marriage is invalid and they have to separate and repent to Allah, only then could they marry again with a new contract.
But if the marriage took place after they repented, it is valid and the couple are not required to separate or renew the contract.
Allah knows best.
You can search for fatwa through many choices