Musnad Ahmad 3:64

Abdullah ibn Bakr and Muhammad ibn Ja'far narrated to us, they said: Sa'id narrated to us, from Matar and Ya'la ibn Hakim, from Nafi', from Nabih ibn Wahb, from Aban ibn Uthman ibn Affan, from Uthman ibn Affan, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The one in the state of Ihram shall not marry, nor shall he give in marriage, nor shall he propose."