Sahih Muslim | Book 10 | Hadith Number 3618

Narrated by Ibn 'Umar (Allah be pleased with them)
Ibn 'Umar (Allah be pleased with them) reported Allah's Messenger (may peace be upon

him) as saying: A person should not enter into a transaction when his brother is already making a transaction and he should not make a proposal of marriage when his brother has already made a proposal except when lie gives permission.