Musnad Ahmad 28:517

Ibrahim ibn Ishaq narrated to us, Abdullah ibn al-Mubarak narrated to us, from Layth ibn Sa'd, Ja'far ibn Rabi'ah narrated to me, from Bakr ibn Suwadah, from Abd al-Rahman ibn Jubayr, that Abdullah ibn Amr ibn al-As narrated to him, saying: The Messenger of Allah, peace and blessings of Allah be upon him, stood up and said: "No man shall enter upon a woman whose husband is absent, unless he has someone else with him." Abdullah ibn Amr said: "After that occasion, I never entered upon a woman whose husband was absent, unless I had one or two people with me."