Musnad Ahmad 30:3719

'Abd al-Samad narrated to us, Shu'bah narrated to us, al-'Ala' and Suhayl narrated to us, from their father, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "A man shall not propose to a woman to whom his brother has already proposed, and he shall not bid against the bid of his brother."