Musannaf Ibn Abi Shaybah

Hazrat Sha’bi (may Allah have mercy on him) was asked: If a person buys a slave and sets him free, and then it turns out that the slave is insane? He (may Allah have mercy on him) replied: If this illness existed before the transaction, then the seller will return to the buyer the difference between the price of an insane slave and a sound slave, and what he has taken, he will keep in its equivalent.

Hazrat Hasan (may Allah be pleased with him) says regarding the person who buys a slave and then sets him free, and afterwards it becomes known that the slave had an illness which originated from the seller, then it is obligatory for him to take back the slave, and it is not obligatory for the seller to return anything.

Hazrat Zuhri (may Allah have mercy on him) was of the opinion that the price should be reduced in proportion to the defect if the illness is discovered after the death.

Hazrat Ata says that after death there is no responsibility.