Hadithcore
Mishkat al-Masabih, 3448

‘Abdallah b. Mas'ud reported God’s Messenger as saying, “Shedding of blood will be the first matter about which judgment will be given on the day of resurrection.” (Bukhari and Muslim.)

وَعَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أَوَّلُ مَا يُقْضَى بَيْنَ النَّاسِ يَوْمَ الْقِيَامَةِ فِي الدِّمَاء»

References1 variant
In-Book Reference
Book 16, Hadith 3