Allah, the Blessed and Exalted, says: "And it is not for a believer to kill a believer except by mistake. And whoever kills a believer by mistake, then (upon him is) the freeing of a believing slave and a diyah handed over to the heirs of the slain." [Surah al-Nisa: 92]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / Q16142