Musnad Ahmad 541:7

Bahz narrated to us, Shu'bah narrated to us, he said: Al-Hakam informed me, he said: I heard Dhakwan, Abu Salih, narrating from a freed slave of 'Amr ibn al-'As, that 'Amr ibn al-'As sent him to 'Ali to ask his permission to see his wife, Asma' bint 'Umays. So he gave him permission, and they spoke about a need. When he left, the freed slave asked him about that. 'Amr said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade us from asking permission to see women except with the permission of their husbands."