Sayyidah Aishah (may Allah be pleased with her) says: I said to the Messenger of Allah (peace and blessings be upon him): "O Messenger of Allah! (Suppose) you come to a valley in which there are trees, one tree from which (animals) have eaten, and you (peace and blessings be upon him) find another tree from which nothing has been eaten; from which of them would you graze?" He (peace and blessings be upon him) said: "From the tree from which nothing has been eaten." She says: "So I am that one," because the Prophet of Allah (peace and blessings be upon him) did not marry any virgin other than me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13472