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 he gives permission.
Sahih Muslim Book 21, Hadith 12
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Sahih Muslim Book 21, Hadith 11 Next Hadith → A Muslim should not purchase (in opposition) to his brother.

Sahih Muslim Book 21, Hadith 13