(13) Marriage
كتاب النكاح
(3a) Chapter: Making a Marriage publicly known, asking Woman in Marriage, and the Condition laid down - Section 1
(3) باب إعلان النكاح والخطبة والشرط - الفصل الأول
Mishkat al-Masabih 3144 
Abu Huraira reported God’s Messenger as saying, “A man must 'not ask a woman in marriage when his brother has done so already, until he marries or gives her up." (Bukhari and Muslim.)
وَعَنْ أَبِي هُرَيْرَةَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَا يَخْطُبُ الرَّجُلُ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَو يتْرك»
 مُتَّفَقٌ عَلَيْهِ  (الألباني)حكم :
Reference : Mishkat al-Masabih 3144
In-book reference : Book 13, Hadith 64