What is the blood money for killing a Muslim by mistake, according to the preponderant opinion and with proof?

If a Muslim kills another Muslim by mistake, he must free a believing slave and pay blood money to the family of the slain as compensation, for Allah Almighty says: "It is not for a believer to kill a believer except by mistake. And whoever kills a believer by mistake - then, he is to free a believing slave and pay blood money presented to his family, unless they remit it as charity." [An-Nisa: 92].