Sayyidah Aishah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "Those (heirs) who seek to kill in retaliation must hold back, the first and then the next, even if it be a woman."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16070