Musnad Ahmad 1153:1459

'Abd al-Rahman narrated to us, from Sufyan, from Abu Ishaq, from 'Amr ibn Ghalib, that 'Aisha said to al-Ashtar: "Are you the one who wanted to kill my sister's son?" He said: "I was eager to kill him, and he was eager to kill me." She said: "Do you not know what the Messenger of Allah, peace and blessings of Allah be upon him, said: 'The blood of a man is not lawful except for a man who apostatized, or abandoned Islam, or committed adultery after having been chaste, or killed a soul without [the killing of] a soul'?"