Musnad Ahmad 30:2211

'Affan narrated to us, he said: 'Abd al-Rahman ibn Ibrahim narrated to us, from al-'Ala', from his father, from Abu Hurayrah, from the Messenger of Allah (may Allah bless him and grant him peace), that he said: "A man shall not outbid his Muslim brother, nor shall he propose to a woman to whom his brother has already proposed."