‘Abdullāh ibn Mas‘ūd (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The first cases to be settled among people on the Day of Judgment will be the cases of blood (homicide). "
شرح الحديث :
On the Day of Judgment, Allah, the Almighty, shall call His slaves to account. Then, He shall judge between them with His justice, starting with the most important grievances. Homicide is the gravest and most dangerous grievance; therefore, it will be the first case to be settled on that great Day. This is with regard to the injustices committed among people. Regarding the slave's own deeds, however, the first deed to be judged upon will be prayer.