Musnad Ahmad 30:2771

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, he said: I heard al-'Ala' narrating from his father, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "A man shall not make an offer on the offer of his brother, and he shall not propose to a woman to whom his brother has proposed."