Musnad Ahmad 435:5

'Affan narrated to us, Hammad ibn Salamah narrated to us, he said: 'Ali ibn Zayd informed us, from Sa'id ibn al-Musayyib, that Mu'awiyah entered upon 'Aishah. She said to him: "Did you not fear that I would set a man for you to kill you?" He said: "I would not have done that while I was in a house of safety, and I heard the Prophet, peace and blessings of Allah be upon him, say—meaning—: 'Faith is a restraint against treacherous killing.' How am I regarding that which is between me and you, and regarding your needs?" She said: "Good." He said: "Then leave us and them until we meet our Lord, the Mighty and Majestic."