Complex sentence: According to Abu Daw’ud, writing a century later, the situation was that a Qurayza who killed a Nadir was killed but a Nadir who killed a Qurayza only paid blood-money.
Split into simpler sentences: According to Abu Daw’ud, writing a century later, the situation was that a Nadir had killed a Qurayza. The custom was that a Qurayza who killed a Nadir was killed but a Nadir who killed a Qurayza only paid blood-money.