Hadith.5372 - Muhammad ibn Al-Fudayl narrated from Imam Ali ibn Musa Ar-Ridha (as), who said
I asked Imam (as) about a thief who entered upon a pregnant woman and killed the child in her womb. The woman then took a knife and stabbed him, killing him.
Imam (as) said: "The blood of the thief is void (without consequence)."