Sahih Muslim Book 8, Hadith Number 3282.

Chapter: Mubrim (one who is in the state of Ihram) is forbidden to marry and the disapproval of giving the proposal (in this state).

Nabaih b. Wahb reported that Umar b. ‘Ubaidullah b. Ma’mar intended to marry his son Talha with the daughter of Shaiba b. Jubair during the Pilgrimage. Aban b. Uthman was at that time the Amir of Pilgrims. So he (‘Umar b. Ubaidullah) sent someone (as a messenger) to Aban saying: I intend to marry Talha b. ‘Umar and I earnestly desire you to be present there (in this ceremony of marriage). Aban said to him: I find you a block-headed ‘Iraqi. I heard ‘Uthman b. ‘Affan say that Allah’s Messenger (May peace be upon him) said: A Muhrim should not marry.