Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that he (peace and blessings be upon him) said: "Whoever is killed by mistake, there is blood money for accidental killing for him, such as when someone is killed by being struck by a stone or a whip; whoever kills deliberately, upon him is retaliation (qisas); and whoever stands in the way of retaliation, upon him is the curse of Allah, the angels and all people, and no act of worship of his, obligatory or voluntary, will be accepted." Amr narrated this hadith from Tawus as mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15884